OTA/TA = total annihilation to most people here just an FYI.
The *A projects are based on OTA. OTA used that sort of tech tree. It is hard to find logic in their choices, mostly it boils down to that they like the spin their favorite *a put on OTA. There are a lot of differing opinions and people get really defensive about their choice. If you like something you like it, others may not. Others may like another *A project because of a random emotional reason. The different *A projects have changed greatly over the past 5-6 years so I am not really sure where they all are and frankly, don't care enough to try them any more

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From what I have observed: Tech A put a bad taste in many people's mouth because senna was piggybacking it into his variants of popular maps. I don't *think* a lot of people still begrudge it for that, but I could be wrong. On top of that many of the BA players are pretentious twats who act like they are great RTS players and require a perfectly balanced gaming experienced(expect a visceral rebuttal of this). So to them, changing things which "break" the years of balance BA has worked towards "ruins" their experience.
I honestly don't play TechA, OTA mods are old hat for me and I am tired of looking at those ugly dated models. <- perfectly illogical emotional reasoning :).
*edit* verbiage changes for clarity