Bitcoin is obviously a very active open source project. So yes, as other have said, it is being worked on all the time and has gone through several major upgrades over the past decade since it became a more mature project and more stable.
It's not like Ethereum or altcoins where a company is in charge and can make any changes they want and they constantly hard fork it for upgrades and everyone just has to go along with it. Bitcoin is decentralized so it is a slower and safer process because it is so much more important to do everything right and with community consensus because Bitcoin is so much larger and more important than any other cryptocurrency. Bitcoin is the one cryptocurrency that can't be replaced if its development were somehow screwed up. So its only every few years there is a major upgrade to the protocol to expand its abilities, while in between there are always smaller updates to wallet software and stuff to make it a bit friendlier/easier to use.
I agree that there is a big difference between bitcoins upgrades and others, but I would also like to point out that ETH has a similar one. I mean sure Bitcoin is decentralized and ETH has Vitalik if we look at it that way, but Vitalik doesn't have any kind of extra power if we look at it technically, he could have some influence over people and convince people but he doesn't have a right to change it himself, he has to still convince people for any upgrade.
This is why I like to say that it's also decentralized. But all the others? I have seen some where there are "owners" of projects, thousands of them and that is definitely not something similar at all.
