I think it's about more than that. Where I love, the caps and bottles are made out of different plastics. Most recycling stations here only accept plastic bottles without their caps, because the caps cannot be recycled. Forcing the caps to be part of the bottle essentially forces it to be of the same plastic. Or that's how I understand it at least, so the entirety of the bottle can be recycled, and so the unrecyclable caps don't end up everywhere creating microplastics as they slowly break down.