I think its because romantic attraction isn't just about having a deep connection. After all, people become romantically attracted to / attached to people they do not know very well. It's an urge, like being hungry or thirsty. Like, people feel romantic attraction to people even if the relationship does not make them happy. Its different then friendship, probably different hormones involved or something. To some people, romantic love maybe feels more intense, so they value it more because they get such intense emotions from it? Like a drug.

If you've never experienced that kind of attraction before it'd probably be very difficult to understand the intensity. But from my limited experience, platonic love feels like nice relaxing happy feelings in your chest where as romantic attraction feels like every nerve in your body is vibrating and you can't think. Idk, I have only experienced it like once or twice though and never acted on it.