I used to think the same thing, but the thing is we don't care about the energy that goes into the sunscreen, we care about the remaining percent that goes into the skin. If you go from a sunscreen that absorbs 98% of the sun's energy to one that absorbs 99% you are halving the amount of energy your skin is exposed to.

If you're still getting burned with 98% absorption, then increasing that number by 1% would actually make a huge difference. And that's without even considering things like having a safety margin for improper application.

what if your skin has a hit point system and that 1% difference is the breaking point of sunburn

Seems like in real world use it makes a difference.

https://www.sciencedirect.com/science/article/abs/pii/S0190962219327550

https://pubmed.ncbi.nlm.nih.gov/29291958/

From another thing I read, people have a tendency to not apply enough sunscreen or apply it correctly. I'm sure if everyone did it perfectly it wouldn't matter. All I know is anecdotally, when I switched to 100 I stopped getting sunburns, and I have been in situations with people who used their own lower spf, got a little burned still, and I came out of it pale white.

The price might be higher, but a quick look on Amazon and I'm seeing more than spf affecting that. The brand I buy is about 1.80 (usd) per ounce, and i see other brands with less spf for more. I see other brands with the same spf for less, and it seems like it's between ~1.10 per ounce to ~2.80 per ounce so I'm not really bothered by my price. I don't know anything about the environmental differences between spf so I won't comment on that.

The average person should almost certainly not be using it, but maybe it would make the difference for extremely sun sensitive people.