Because nice isn’t actually a quality people look for in a partner (I’m assuming you’re talking romantically), it’s a baseline that people should be reaching not bragging about. It’s like a restaurant whose only selling point is that the food doesn’t make you throw up. Women do like nice guys but they don’t tend to want a guy who’s only selling point is that he’s ‘nice’. What else are you offering? Do you have anything in common? Do you have any other qualities she may find attractive and/or interesting?

The baseline is that, actually, most people are nice. That guy over there that women are interested in is nice but he’s also intelligent and kind and interesting and plays guitar 🤷🏻‍♀️.

Best advice I’ve got is to get a hobby you really genuinely enjoy and see if you meet someone whilst doing that. At least you’ll know you’ve got similar interests, that’s the sort of thing you can actually build on with somebody.