Why is Jolteon rated higher than Flareon?

Probably because in the prior and current metagame, electric is arguably more useful than fire. Gyms used to be stacked with Vaporeon and Gyarados, which fall to Jolteon easily. Also, there just weren't that many good electric options prior to the legendary birds. Jolteon was the undisputed electric go-to. Flareon is fine, but when was the last time you saw grass or steel stacked in a gym. Also Arcanine, Charizard, and Typhlosion can be decent alternatives.

Jolteon is superb at one thing- slaughtering Gyarados. That's all it needs to do. Also good performance against Vaporeon. But he is also a OK choice against all the birds - remember there are five of them!
As for Flareon, you only use him in Articuno Raid.
So by utility, Jolteon is more useful.

Not sure ratings are updated.
Simple answer: because jolteon is/was very relevant in the metagame as a specialist, whereas flareon had/has very few match ups where he is useful in real life.

Edit: it's probably up to date and the higher rate is also because jolteon is great against the birds as it was already mentioned