Because we have shipped products with those and boy I wish we had used Linux instead!
Limited, expensive, developer unfriendly and surprisingly, quite unstable under certain loads.
I believe you the developer experience was years behind Linux. That doesn't invalidate my claim that microkernels are interesting (and that these two are innovative), unless your pain was explicitly due to the microkernel nature of things.
But just last month we have had some _serious_ issues with QNX (which is supposed to be the top dog ukernel in 2023). For example IPC performance takes a nosedive in certain (not very uncommon) situations, which is not good for an RTOS. Talked to other people working with QNX and they have had similar problems.
Linux in a similar product has worked far far better. I understand the hype around microkernels and all that, but there is a reason they are not used in anything but the most basic products.
Because Hurd is (in my understanding) exactly the solution in search of a problem you're talking about. It's microkernel for the sake of being microkernel, but tied to the past (POSIX/UNIX model).
Actually innovative microkernels can do things Linux or other mainstream monolithic OS can't just copy (and that's why they're interesting).
Again using L4 as an example, have a look at discussion here: https://news.ycombinator.com/item?id=35842240 (but there are also other interesting designs, eg QNX)
Nobody forces you to switch to a differnent OS, but that doesn't mean it's pointless to research and build different systems.