There really is a quite a bit to creating even simple sample libraries. For the most part, Kontakt is pretty universal these days and that’s always a good place to start. I’ve created (and sell) some simple libraries that I built from scratch and even those were quite labor intensive.
For sampling hardware synths (and even acoustic instruments), I’ve found Sample Robot to be quite a valuable piece of software. You still have to do a lot of work by hand but there are certain processes that it helps out with quite a bit.
I think that rare and unique instruments fall through the cracks quite a bit when it comes to sample libraries. A lot of smaller companies have been filling in the cracks during the past handful of years, though. Andrew Aversa and the folks from Impact Soundworks have done a really nice job putting out some quality stuff.