For the same reasons why Google did it in the first place.

To not undermine trust into their product and because ads are lower quality than organic results, and by making them indistinguishable, it will make their product worse.

The chatbot market is still competitive, and while users may tolerate ads alongside their answers, they may not tolerate lower quality answers (that is ads disguised as answers). With Google search, they can get away with it because they are still the best even with the enshitification.

There is another reason why it is in their best interest to make it really obvious there are ads. Chatbots want you to pay directly, sometimes hundreds of dollars a month, they are not getting that kind of money with ads, so obnoxious ads are also a way to say "hey look, if you pay, you won't get ads". It doesn't mean ads won't make a comeback in paid tiers later, but not initially.

So, yes, lots of "probably", but my guess would go towards the first ads being obvious and flashy rather than subtle.