Several reasons:
1. They have internal data that suggests that investment is worth it - maybe Florida isn’t as far gone as many on here seem to think. In 2016 even though FL was only 0.4% to the right of WI, the Biden team seemed to deprioritize it as part of their path - they likely knew better than we did that Dems were struggling in the state. I’d also remind folks in 2020 Trump “only” won Florida by 3%. That’s historically a decent R win by Florida standards but isn’t some kind of mega landslide victory. And sure one can point to FL in 2022 as proof the state is going hard right, but Dems landsliding in PA and MI doesn’t seem like proof those states are in the bag for Biden.
2. Recency bias. Obama won FL twice when Biden was VP - just because Dems have seen a path to winning statewide in FL presidentially in relatively recent history, they see it more optimistically than a place like TX where a Dem statewide win hasn’t happened for a long time.
3. Biden team just has a lot of money. Campaigns are never spend money on the 5 main swing states and nowhere else - it’s good to diversify to make multiple possible paths to victory and also help downballot candidates. FL-Sen could very realistically be the Senate tipping point and Biden knows keeping the state close keeps DMP in the game.
4. This ties into the last point a bit but spending money in Florida forces the Trump team to spend money there - especially with Trumps ego he probably wants to prioritize a large win in Florida and any money Biden spends in FL is a threat to that.
Could easily be some combination of these factors
Also what if the 2022 FL results were a bit of a flash in the pan? Poor turnout? "Popular" R candidates (Gov and Sen)? Media exaggeration turning into self-fulfilling prophecy?