Why do crocodilians still have legs?

They are evolving as should be evident through simply observing the utility of those legs. You will wait quite a while to witness a crocodile run down an antelope.

Alligators can actually run 17 miles an hour on land. I’ve never wanted to put it to the test.

To guide the body around obstacles, other croc’s etc
On land they can catch prey as their prey are drinking in the pools of water.

Crocodiles live in regions where water sometimes dries to mud.
That’s a time when legs are handy.

I also think legs are useful. I guess the natural follow up would be why don’t we see crocodile-like mammals that are kin to cetaceans if it’s such an effective strategy? Seals?

Crocs are an extremely successful group, sole survivors of the large reptiles from the age of the dinosaurs and virtually unchanged in the eons since.

They use their legs to build nests and chase prey on land

Where else to put on these classy crocodile leather boots?

Apart from anything else, their legs are used to kick sand/soil when burying eggs.

Here, under “Characteristics” and “Hunting” it describes how their legs are useful to them:

https://en.wikipedia.org/wiki/Crocodile

Legs make it easier for the males to boink the females.

I am assuming that since they are cold blooded, that they regularly have to come ashore and lay in the sun to warm up their blood.

Evolution. It still happens. Come back in 29 million years and ask the same question. The answer will be different.

No legs call ‘em Gars

They also need them to burrow underground to have babies and stay cool. And I believe they can hibernate during times of drought.

What alligators and crocs will do, also, is when they kill something that’s too big to eat, like a deer, they will bury it in the mud for a week until it gets nice and soft, and then they eat it. They need their legs and claws to bury it in the mud.