I don't understand how people can compare the number of players in tf2 to games like cs go, in cs go most of the players that play understand their objective and know what needs to be done regardless of how good they are.
in tf2 I am not even sure half of players that play at any time knows what they are doing, and you can easily see that if you join valve servers.
investing into this game might only bring people that are pub stomping, and are not yet familiar with competitive tf2, which is also rare.
and another thing is that even the people who are familiar with it don't seem to like it because all they care about is why their main class isn't being played more instead of understanding what are the best classes to be used during the game.
making tf2 a successful esports requires an unbelievable amount of resources and time, so that's why valve brings shitty no effort updates just so it will look like they care and want the game to succeed, tf2 was one of the first games with trading on steam and with the steam market implemintation valve are earning a lot of money from tf2 and thus don't feel obligated to change anything about it.