why isnt a crocodile sentient?

Technically, it is: https://en.wiktionary.org/wiki/sentient (the first two definitions). You mean the science fiction definition though (the third), and it's because it's not self-aware and not very intelligent, because it doesn't need to be to survive and procreate successfully. A slightly smarter crocodile must not have enough of an advantage over its peers to matter for evolutionary purposes.

Honestly, I do not think high-intelligence is useful for life. The most successful life forms aren’t the most intelligent, and humans seem to be fixed to self-annihilate.

what do you consider the most successful life forms to be? humans currently inhabit every continent and are unquestionably at the top of the food chain.

Are we though? Bacteria do better than us. Cockroaches. Rats. Ants. Grasses. Plankton. We aren’t the most numerous. We aren’t the most widespread. We are serious risk of killing off our own species.

If the Earth was about to be hit by a huge asteroid, some people might survive (by fleeing in spaceships) but none of the species you list have a chance unless people choose to save them.

I highly doubt much of the bacteria would care. The amoeba probably wouldn’t either. Also, rodents have already survived such impacts. All mammals alive today are alive because our ancestors didn’t die with dinosaurs.

Suppose the asteroid is much bigger than the one that ended the dinosaurs.

If the Earth is completely destroyed, the humans on space ships wouldn’t survive either. There is no self-sustaining off world colony currently, and there most likely will not be in the lifetime of anyone alive today. At such time that there is, bacteria, rodents, and other life will likely come with humans as humans build the biospheres that we need elsewhere.

With a few years to prepare, the humans would have a chance IMHO.

Who says they aren't? Of all the reptiles, they seem among the smartest.