AimIsADickSeriously what's wrong with the idea?
i guess i can be the one to take u seriously and present the impossibly obvious answers
main problem is that about half of non-slav europe (250m+) already speaks english conversationally, and the ratio is certainly much higher in younger international online communities. esperanto has probably fewer than 100,000 fluent speakers globally, with many of those in SEA. asking what, 10-20% at most of tf2 euros to learn conversational english is less demanding than asking 99.9% of tf2 euros to learn esperanto
also keep in mind youd be asking those 99.9% to learn a new language purely to comm in tf2. they would still want to learn english to be able to communicate with foreigners in the real world. even if people wanted to move to an easier-to-learn, more structured language then spanish would be a much more useful alternative
english also actually works really well as an auxiliary language, at least for europe, mostly due to the elasticity of its grammar, but also from broad similarities to germanic structure and romance vocabulary. esperanto is probably also fine, but if you look empathetically at the real world usefulness of language, its only real advantage is ease of learning. if you wanted to talk about a global auxiliary language then its worth discussing constructed languages but thats not rly relevant in tf2
should also be noted that 95% of the problems ive seen about language barrier in euro gaming come from slavs (who have a different standard language) playing on euro servers, and most of the rest are about french people refusing to learn english