An infinite timer is useful in modes like Gungame, DM, and CTF, where players can actually win by achieving the target score/kills. It can be quite annoying for CTF games to end in 30 minutes thanks to the default timer. I'd made a suggestion about adjusting default timers a while ago. Maybe it'd help end rounds within an appropriate amount of time.
I might be biased here, but this is just another way of depriving us of certain popular features that were removed after v7. Infected, CTF, DM, and Gungame are great in big rooms. If some people don't like big TDM rooms, they should simply avoid them rather than taking away the option from others who enjoy them.
I don't generally find the garden or atk & def crowd playing small TDM rotations in 5 maps on repeat for long - they just quit or join training rooms. People with the constant serious/"oldgen" mentality who consider everyone else "questers" or "randoms" aren't the only ones who play, so it's only fair that all kinds of players have the options to do what they like. Variety makes this game fun.