This is pure speculation on my part, but it's likely that Cakewalk's server data will be moved to and consolidated into a new host, one of BandLab's choosing. That would include the customer database, the download cache, the authorization software, code projects, and this forum. So yeah, if you want your personal presence to make that move along with everything else, it's a good idea to establish an account with BandLab.
They may also need to import some of that data into other databases, in which case your email address is your unique identifier that'll make it possible to correlate old and new data. So you'll want to use the same email address as in your Cakewalk account. Although unnecessary, it's a good idea to use your same forum handle as well, just so we'll all know who's who on the other side.
Plus you don't want some joker registering over there under your name. Not that I'm suggesting there are any jokers here.