Q.My hibiscus looks healthy, but hasn’t bloomed in several years. What’s the problem?
It came to me potted, and I’ve re-potted in bigger pot. I’ve mostly kept it indoors in my sun room where other hibuscus thrive. Some summers I’ve had it outside in the pot.

Certified GKH Gardening Expert
Does your hibiscus get plenty of sunshine, water and fertilizer? Odd that your others thrive and this one doesn't. Has the soil ever been refreshed in the pot? You say you repotted to a larger size. Hibiscus like to be a little crowded so if you moved it to a much larger pot, that could be the problem. Also, inspect the leaves closely for signs of insects or disease.
Here is more information that may help.
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/deadheading-hibiscus-flowers.htm