Why won't my cherry tree fruit?

What variety is it? Some varieties of cherry need a different variety nearby to pollinate them. Almost all old cherry varieties are like that, whereas most of the newer ones like Stella are self-fertile.

Probably a lack of a pollination partner nearby, or the weather (or an exposed location) not favourable to bees at blossom time, or weather damaging the flowers so fruit can't form.

If a tree is small bees often don't bother to visit. Bees prefer bulk harvesting from large trees with thousands of flowers just as we prefer to do our weekly shop in one time-saving car full.

In the last few years bees have been non-existent when my pears flower, with the result being very few fruits or none at all. This year my pear crop will be almost nothing due to lack of bees.
It's getting to the point where I'm thinking of removing my pears because of the lack of bees leading to consistently poor cropping.

My apple crop is nearly always satisfactory but by the time my apples flower the little solitary 'orchard bees' have appeared along well as decent numbers of bumblebees so pollinating insects are plentiful at that time.

I don't use any chemicals of any kind at any time so it's not me poisoning the bees.

The cherry crop in this area is OK this year as is usually the case. No need to grow cherries here because there are many large old trees in this area - they thrive here and seedlings spring up all over the place.
However, I know someone with a big old ornamental cherry which every year produces lots of spectacular blossom but never a single fruit which I'm assuming is a genetic abnormality in whatever variety it happens to be - perhaps that's a desirable characteristic of an ornamental tree so the owner doesn't have to deal with fallen fruit, bird poo and stained washing/cars/paths.