I think it was pretty widely understood that he was going to have to be adamantly in the race until the exact moment he wasn’t in the race. The second he showed any public wavering it would have been over.
I can understand that perspective too, but a problem with that approach is that he might seem arrogant and out-of-touch - and I would have difficulties trusting a party who is so clear in their communication for so long, and then abruptly change direction completely
This is how it works everywhere. Do you go to your boss and say "well, I'm thinking of quitting and taking a different job, but I'm not sure yet and I'm still deciding. I'll let you know when I've decided!"
resignation and successful impeachment rates are pretty low, so basically it's 4 years, and then later basically one can do whatever they want, they instantly have an amazing audience/market.