I would say that a) squeamishness about eating certain animals/animal parts and b) more sentimentality towards animals must be two big reasons why horse is consumed less in the UK.
I have only my own observations to go on, but it is certainly seems to me that the average French person eats and enjoys a wider range of meat and seafood products than the average Brit. At my supermarket you can buy big buckets of pig trotters and snouts, huge whole cow tongues, fresh tripe, whole rabbits, kidneys from various animals, veal, horse, not to mention oysters, mussels, squid, crab etc etc. While the trotters and snout are probably for more of a niche market, I think still the majority of French people would eat and enjoy veal, horse, mussels, oysters, kidneys, rabbit etc in addition to the regular beef, chicken, pork, lamb that are the staples of UK cuisine. And food is more classless here too.
It also seems to me that the average French person is less sentimental about animals (even pets, often, I think) and cares less about animals' quality of life, except insofar as it pertains to whether it affects the taste of the end product.
Foie gras, for example. Over the years I have asked dozens of French people if they feel guilty about eating foie gras given the way it is produced. The response is practically universal. Their face will momentarily cloud over as they acknowledge it isn't very nice. But then a smile will appear as they come to the final and overriding conclusion 'but it tastes so good!' End of story 