Because a real diaphragm (or piston with gasket seal) and retainer would be too expensive...
There are conversions around to
replace the waste ink pad with an external bottle; you can't get around the waste however as the cleaning process involves sucking ink through the nozzles to unclog them.
I think the existing scheme could have been made a lot more durable, and not much more expensive, if there was more plastic for the membrane to be glued down to. The rim of each reservoir is very thin.
I put quite a lot of Araldite around the circumferences of the other membranes, so that should help seal them up.
I read that the Epson printers count characters and after a fixed number tell you the ink is empty,This applies to all characters so if you print nothing but full stops when you achieve the magic number of x thousands the machine stops due to no ink despite the cartridges beefing virtually full still. Reset the chip and you can start printing again, I have never tried printing all full stops but have reset a cartridge and been able to print another 50 plus pages.
I don't know what the specifics of this model printer are, but from now on whenever I print I will just make sure that the color option is set to either B&W or grey scale. Hopefully then it will not decrement any counters for the color inks. I'll just have to see how it goes.
Yellow will still be used as it is the colour used for the secret stenographic serial number printed on each page. At least now you have a stealth printer.