They are not supporting MotoDev studio anymore. This has to do with the restructure after the purchase from Google.
I am not sure about downloading legacy builds, but Motorola isn't actively developing this anymore (and laid off most of the team that was working on this).
You might search for "MOTODEV Core Plugins", as they renamed studio to that - but you probably want to not use these tools anymore, since they are not being supported moving forward.
