Teambuilder was soooo great!
No... No, it wasn't. It was a >5 minute queue where people wouldn't let you try new things and nobody wanted to play support or jungle. Time to grow up people. Time to learn how to play some more roles. Every champ is playable in more than one role, so you can still "main" your FOTM champ. Just take brand support... or mid.... or jg... You know what, take brand adc. At this point it may be viable.
The way that team builder went was not the way Riot was expecting it to go. This switch is bringing it more in line with their original intentions, which were to force players to play more than one role, ultimately reducing toxicity when some 10 year old doesn't get mid for his 100th game in a row.