Love at first sight is one of those things that's very rarely, if ever, found in life but it's found in books all the time. There's a good reason why authors make characters fall in love instantly: it takes a whole lot less time and energy to write. But love at first sight can be done well...if you're willing to take the time to do it.
The Day I Met You
Love at first sight is a common love stereotype you'll find in novels all the time. It's much easier to make characters love instantly than it is to fill up pages and pages of a relationship. Actually falling in love takes so much time and trouble, there are entire books just about falling in love. So when you have to fold a love plot into a story that's already packed with other stuff, love at first sight is an easy and attractive option.
But it can also be a lazy option. That's why you've got to put in the work to make sure it's done well.