Why don't they sell frozen tomatoes like other frozen vegetables and fruits?

There is no advantage to freezing over canning, and from many perspective there are disadvantages (discolouration, mushiness, overall general cellular destruction)

The embodied energy required to can is also much less than to keep them frozen, so this combined with disadvantages of freezing tomatoes, manufacturers choose to use canning

Yes, you can freeze dry tomatoes into a powder, it's not that great compared to freeze dried fruit powders though

Dried tomatoes (think sun dried tomatoes) are excellent, but are generally not a useful substitute for fresh tomatoes

They are :) (site in French).

However, if you look at the reviews, the average customer isn't too pleased with the product, essentially for the reasons mentioned by @PatSommer (watery, poor texture, etc.). Don't forget that canning transforms tomatoes in a way which makes them particularly useful for sauces and the like, which is another reason why it is such a popular method of conservation.

Beside the reasons in the other answers, tomatoes really don't like low temperatures. They change their aroma and texture already at fridge temperature. They will go through the same temperature region when freezing and thawing, so they will get that bad taste of a cooled tomato. They won't have the texture of a fridge tomato though, because the freezer will do a larger change - instead of getting unpleasantly hard, they'll get limp and their juices will separate.

To sum it up, canned tomatoes don't taste like fresh tomatoes, but at least they taste like cooked tomatoes. Frozen then thawed tomatoes don't taste neither like fresh, nor like cooked. They are just not that good to eat.

Frozen tomatoes will lose all their structure, so are only of use for cooking. Canned tomatoes works very well for cooking and are cheap. The taste is also improved by the canning process, but not by freezing.

So I can’t see how anyone can charge enough for frozen tomatoes to as to make a profit.

But I have frozen my own tomatoes. To do so, blanch them in boiling water, or cook them down into a source before freezing.