There's a lot of reasons to buy a boost in 2019, you improve at the game when you play in higher elo, sometimes you are stuck at your elo just because you played too much that your matchmaking is cursed(that means you will get flamers, inters and bad players 90% of the games), you don't play the game too much but you actually want to play in higher leagues, you want to be cool infront of your friends showing them you are high elo with insane winrate...like i has improved in low elo because i can see my mistakes, people improve in higher elo because they can see their mistakes, that's the main point of boosting (as my opinion), but everyone have their own reasons (and all valid) to purchase a boost.
^^ I highly disagree with you, i am a main grandmaster on EUW, I can assure you, that match making has nothing to do with whatseover were you are , "elo hell" is such a 2015 meme joke, i got around 50 players on my friendlist, and they all are D1-challenger, i can assure you 10000% that if they were to go into gold 3 they would just like a booster win every game, and they will meet the same matchmacking you do, it's simply a question about skill and being good or average or bad at the game.
People improve in higher elo, ? yes and no if you ACHVIED HIGHER ELO BY YOUR OWN : then obviously the anwser is YES , if you PAID for it ,you will drop faster than a clintons hangies , because you will be outclassed and simply destoryed in every lane you go to, what would teach a player would be coaching, boosting only destory ranked games and the game itself, th showoff? sure, i mean if that's what ... make you feel cool in life? sure, i mean you can buy a challenger account right now on serval respected sites for around 2-350 usd . sure if that's your goal in life, to impress other with elo ..? okay.
Lastly i think the most important thing in ANY thing in life that has to do with skill or goals , is the feeling that you acutally achivie it ,you acutally worked it for i, picture going to challenger by grinding and learning for 2-3 seasons , and finnaly get there, or > go pay 1000 usd for boosting, i guess we look different at it