There would be more supports if the people who played support wernt, still are by many, talked to and treated like slaves or a bag of wards. Also if the people who HELPED you win matches got recognition more often for being good at supporting.
The carry that gets 17/1/9 stats gets honors and praise and friend request, the support that 100-50 initiates, then CC's them so they cant get away, soaks all the retaliation for the first 6 kill of that carry so they get fed then goes on to get 2/3/31..... they get maybe an honors from the ADC they got fed... maybe.
There is just as much at play as being a good support, or more as any other role. You have to have the combat skills to face off in a lane with two people who can dive you and your lane is prime target for ganks. You need to zone the enemy ADC off farm, and stop the enemy support from zoning your ADC, you need to ward well to protect your lane, you need to know when you can roam as in will it be better to stay and protect the ADC or pincer gank mid with jg coming from top? If the ADC had to back, or died you may even need to be decent at last hitting minions that will die to the tower. There is no skill or mechanic in this game that the support dosnt need to know how to do, or wont be called on to use potentially in a match aside from perhaps efficient jungle clear routs.
Good supports who master their role help their team win in lots of small and many big ways, and at the end of the match, no one gives a fuck.
So its not popular for that reason, but anyone good enough at the game to do every support skill well, is also probably good enough and smart enough to know that carrying the game on your back is a more reliable way to win than doing an AMAZING job of supporting a fucktard who will never carry the match theyre in. Just like the runny liquid shit that is some peoples skill level at this game that que up as ADC, you cant carry them as support cause it just keeps slipping between your fingers. When the ADC starts feeding up the lane, then you die a few times cause youre trying to defend the turret, the rest of the team blames you as much as the feeding ADC its "BOT LANES FAULT!"
Support is also a role that needs teamwork, and most of the people who play this game are younger kids. Studies show (here come the downvotes, happens every time and sorta proves my point) that kids are selfish and self absorbed more often than not. This means giving up on the glory of carrying the match to "help others" isnt something they like to do.
Check my match history, I main primary support in ranked, secondary top, which means I main support in ranked. I have a positive win rate. STILL, I get ADCs that are total trash that talk shit to me like Im the problem in our lane. Id like to play top form time to time... but with the state of the support role, there wont be a lot of people trying to take it from me any time soon.
https://www.youtube.com/watch?v=jGy5ZJ8cSUE