Sega has stated that 2021 will be the next big year for Sonic, and having yet received any tangible sign of things to come, many fans have been waiting in restless anticipation. After the disheartening turnout of Sonic Forces in 2017, which had a similarly long and quiet lead-up, the precedent was set that whatever's next may not even be worth the wait.
A Sonic Adventure remake is what often gets tossed around as a rumor and the remake-happy climate of video games currently makes it seem like the right time.
Not to mention it's the perfect place for 3D Sonic to realise the value of it's early design concepts.