So, basically how Active works is either you license the technology and host it on a private/proprietary server or you allow Active.com to host it for you (thus, saddling them with the responsibility for covering security, bandwidth, etc. etc. that comes with hosting a purchasing/registration database of this sort), but allow them to collect fees on top of registration. Either way, Active is getting a cut from the races - currently, it's all of us runners that foot the large part of the bill.
That said, the Active platform does provide a lot of useful - albeit non-proprietary - features ... like automating bib distribution, the verifier tool for Proof of Time, as well as a historic database of registration data. I don't think RunDisney would be dumb enough to try to build & maintain their own platform when one is readily available for implementation on an existing web platform.
But going back to maybe Princess? of last year, RunDisney has slowly started migrating documents and things from the basic directory on RunDisney.com to a secure platform housed within Disney.Go.Com (the secure directory for Parks & Resorts). There are other reasons that RunDisney might license the technology and house it privately as well ... first being unfettered access to data mining (ie. now, RunDisney doesn't have to share any registration information or personal registrant data with Active.com, nor are they required to have an opt-in to receive messages from Active.com to conclude registration), as well as expanded communication opportunities - like higher levels of whitelisted emails (newsletters, race-specific mailings). Starting with a STRIDE Newsletter in September 2017, and going heavily through W&D and Marathon Weekend - all emails and notifications switched from originating via the Active.com email system to being sent by a new RunDisney email address under the Disney Destinations email account. This easily explains why we've been receiving more and more emails from RunDisney than ever before - it's because mailboxes recognize emails from DisneyDestinations.com as more reliable than something from an annexed .active.com email account.