I disagree with your assessment that "it's not half as bad as when Rigol produces a new product". The bugs discovered in things like the Rigol scopes and function gens are minor. Very minor.
"Minor", seriously???
Have you looked at the various nasty issues the DSA800 had (lockups, Power Sweep and other stuff non-working)? Or the long list of bugs the DS1000z and the DS4000 Series suffered when they came out (and they still suffer from many of them)? There are very long threads in this very forum, which are pretty hard to ignore.
People can forgive some of the bugs because of the low price, but reality is that most big brands would be ashamed to release devices with such immature firmware (not saying it never happens, but when it does it's an exception while for Rigol it's just normal).
You're talking about engineers who tend to be pedantic and excruciatingly detailed and technical, and will whine about a bug that makes a reading inaccurate, when they may never use that function and would never have known about the bug unless told.
What silly drivel.
For one, the people who tend to buy Rigol are mostly hobbyists and beginners, and they are usually much more forgiving towards those problems than experienced engineers. Do you really think any professional would accept that some of the functionality of what at the end of the day is a tool doesn't work or works erroneously? No serious lab would waste valuable engineer's time to work around flaws of a cheap piece of test equipment. There's a reason why the big brands still have a strong foothold in the professional sector, with cheap brands like Rigol or Siglent being close to irrelevance even when looking only at low end test gear.
Second, and more important, it is completely irrelevant if a device is owned by a pedantic person or not, or if the owner actually needs a specific function or not. Any buyer can rightfully expect that the functionality that was promoted works correctly when the device was bought, and not at some arbitrary point in the future. In many countries this is even by law. If you're satisfied when functionality in a product you bought and for which you paid for doesn't work then more fool to you.
I get that you're obviously fascinated by Rigol kit, but the main reason some Rigol kit is worth buying is because it's cheap, and good enough for modest requirements of most beginners and many hobbyists, and because of the low price and because for them electronics is just a hobby and not a way to earn a living, they can usually live with the fact that the kit is buggy and that they will have to wait for problems to be fixed.
Rigol was the first to get price/features right but isn't the only one. Siglent offers mostly similar kit in this class (and for some things like low end AWGs even has a much more attractive portfolio than Rigol), aside from the DS1kz (and I'll guess we'll see some competition there, soon).
Well, from the test equipment sellers I know well enough to talk about sales - Rigol is destroying Siglent in sales. So the market doesn't agree that their portfolio is much more attractive, or even more attractive at all.
More hyperbole? Your electronics cornershop may sell more Rigol kit than Siglent, but the fact is that most of Siglent's kit is sold under the label of other brands, from bottom-of-the-barrel names like Atten to Teledyne LeCroy. Rigol kit these days is, well, sold as Rigol (I think Agilent/Keysight stopped sales of their Rigol rebadges a while ago).
Also, while Rigol's DS1054z scope is a clear winner as a beginner's scope, other Rigol kit isn't necessarily as attractive. For example, for low end AWGs Rigol still only offers the outdated DG1022U which looks pretty poor against the Siglent's SDG800 and SDG1000 Series of AWGs, which happen to sell really well. And Rigol's more expensive kit is even more unattractive, i.e. the DS4000 and DS6000 scopes (which are pretty awful offerings in this class and price range), which is why they sell pretty bad. The Rigol DG4000 is a decent AWG (although like other Rigol products it arrived with embarassing bugs), but the same can't be said about the newer DG1000z Series which is pretty expensive, and again suffers from some annoying problems.
Rigol will come up with new products when they feel the need for it, i.e. when there are more similar products and sales figures will drop. Until then they'll just sell on what they have now.
Yes, like every company in the history of commerce does. The only companies that engage in R&D for the sake of it are those run by engineers who are shitty businessmen and they tend to go out of business quickly.
First, Rigol doesn't do "Research". Nada, zilch. They certainly do "Development" but all based on cheap standard COTS components. Most of their effort is probably limited to the case/shielding and the PCB layout, plus the firmware. This is why Rigol can be so cheap.
Companies that do "Research" usually do it to push technology further which gives them an edge over their competition, plus it increases the company's patent portfolio which can be helpful in case they are sued for infringement. But "Research" costs money, money which in some cases the company will never (fully) recover if some new technology turns out to be a dead end.
The fact that Rigol mostly uses cheap components to create simpler and cheaper devices is perfectly fine, and products like theirs obviously have a place in the market. But it's silly to think that they have similar long and complex development cycles like the big brands who do a lot of research and design their own ASICs.