I always got the impression, similarly to you, that Sony let their devs do their thing. Most creatives want to move on, eventually. Nobody wants to be known for just one thing and never evolve. Naughty Dog, as an example, moved on from Jak because they wanted to try something new. I like to think Sony MOSTLY respects the creators enough to not want to disrespect the IP.
And seriously, there's something of value to be said about knowing when it's time to move on. Uncharted is a great franchise but I'm happy to see them move on. I'd be completely satisfied if 4/Lost Legacy was the end of that franchise. I'm also happy if Bloodborne doesn't get a sequel. Not everything needs to be Franchised.
@JWeinCom, your statement about Naughty Dog and Insomniac selling Crash and Spyro then moving on is wrong , Mark Cerny was given in his words a bag of money to start up Universal interactive and needing content he approached ND who were renting space on the universal lot and offered to fund their next game in return for the IP that IP went onto become Crash. Cerny did the same deal with Insomniac who were also on the lot, so both IP's became owned by Universal before they were even made, Sony came into the picture much later when they saw Crash at a developer fair and arranged the playstation publishing deal.
The rest of your reply is spot on with them allowing developer freedom and looking at the games that followed it paid off in spades.