Genuinely wondering, as someone who is not a web developer: is React the reason why most websites are so heavy and slow? As in: is it the default because it ma

Genuinely wondering, as someone who is not a web developer: is React the reason why most websites are so heavy and slow? As in: is it the default because it makes developers more productive, but at the cost of slowing innovation that would make websites less heavy and slow? Or is "innovation" here completely independent from the performance?