They're not and they'll forget you as soon as you leave (and you, them).

This may well be true in lots of places; I wouldn't know, having only limited working experience at this point. But I worked for a while at a startup of 5-10 people, and this was very much _not_ the case. Perhaps it was the size of the company. I still have good memories of working there (even if the application domain eventually proved to not suit me well), and even now I have mostly-inactive but still very friendly contact with one of the founders.

There are also good people on this planet.