Certified GKH Gardening Expert
Did they bloom last year? If they did, there's a chance that's all you're going to get. Tulips need hot summers and cold winters, and a lot of garden environments just aren't that suited to them. Gardeners in these places usually have to treat tulips as annuals.
If they've come back successfully in past years, there's a chance they were cut back too soon last summer. Tulip foliage needs to fade naturally to give the bulbs a chance to store up enough energy for next year's blooming.
It's also possible, like you said, that the bulbs are overcrowded and need to be divided. This is more likely if they've been growing in the same spot for a few years. Wait until the fall, when the foliage dies back, to dig up and divide the bulbs.
There are a few more possible problems and solutions in this article, if you're interested: https://www.gardeningknowhow.com/ornamental/bulbs/tulips/tulips-bloom-every-year.htm