I am under impression Keysight invests in top tier oscilloscopes and does not care about Siglent or Rigol.
We have a saying here which goes like this:
What does the oak tree care if a pig rubs against it...

Keysight has had a completely different clientele for decades.
If you're still making enough money with it today, why bother with low-end products?
LeCroy seems to do similarly, just shamelessly rebrands Siglent for low end models.
What do you mean by shameless? In my opinion, it's a kind of concession to have something like this on the shelf in case someone asks for it.

They don't make any money out of it.
At the moment Lecroy, Keysight, Tektronix have nothing to worry about
They have nothing to fear from Rigol, it's a different story with Siglent, but it will be some time before they become a serious competitor, in the sense of poaching customers, not in terms of technology, which is already not of bad parentage.
R&S, on the other hand, are doing a clever job with their portfolio.
They are already a bit further ahead than the other "big" providers.