And that customer experience is really hard to figure out, so it makes sense to invest in a lot of things to improve your chances of finding the winning solution. And there is always the possibility that there wont be a single winning solution anyways.
Enough abstraction, let me throw out some examples:
PEVs carry a huge battery that takes up a large chunk of the car's base. So one bump and that battery is now damaged. But a fuel cell is much smaller, can withstand a bigger fender bender. That may be 10x more important to customers than some theoretical optimum.
Here is another:
Batteries may not be as long lasting for customers that want their car to last 20 years (current expectations, barring getting run into). Exactly how long lasting on the road are the current batteries? Do we know what service costs they'll have compared to fuel cell service costs? Will they survive well in different climates/humidity/dust, etc? So maybe a model with a battery that is more serviceable and cheaper will outcompete a model with a battery that is more efficient, and a longer lasting fuel cell might outcompete both.
Time to recharge is a lot more important than range. I can charge my gas tank in less than 60 seconds. If it takes an hour, then range doesn't mean the same thing. Who hangs out at a charging station for an hour? So being able to charge more conveniently may be a lot more important than range or the number of charging stations. What will win out? We don't know, so cover your bets.
Yes, there is cool new battery tech coming out. I hope we get even more innovation in batteries, it is hugely important. But will the cool new battery tech be affordable, durable, long lasting, fast to charge, and able to operate reasonably well in a place with 4 seasons and lots of rains, in a car that drives for 10 years on lots of potholes and gets into a few fender benders? Not so clear. So don't put all your eggs in one basket.
It makes perfect sense that Toyota is experimenting with lots of alt-drivetrains, even as it cranks out gas and diesel cars and they came up with a much better hybrid model as well. As far as I know, they have everything covered. Ultimately the consumer is going to decide what they want to buy, and the market will respond to that. The question is whether you will be able to respond or will it be someone else because the hot thing is X and all your R&D was sunk into Y. Toyota is trying to make sure that whatever customer preferences happen to be, that they will have solid contender in the mix. And in the end, whatever gives the customer the most convenience, performance, affordability, and durability will win, and Toyota wants to win.