They could of course but they wouldn't.
You already know the reason.

Even I didn't think Sega would be that greedy. They're not
that greedy, but still unbecoming of them.
Oh yeah, I forgot that puberty changed how people sounded.
If he's recasted, adjustment must be done with auto machine which changed his sound to be kid-like again.
To be honest I won't mind if Classic Sonic's being voiced by new sound entirely.
I just don't like that he's mute.
They likely chose Classic Sonic to be mute because it was back before voice acting in video games became common.
But yeah, I wouldn't mind Jaleel White reprising the role, but would he allow his recorded lines to be digitally pitched afterwards? Would he be insulted if they did?
Sonic Adventure's actually one of three Sonic games (besides Sonic Frontiers and the first Sonic game on Mega Drive) that's been successful in Japan.
So popular that it got an additional event exclusively for Japan where must find five photographs of real hedgehogs placed throughout Station Square within a ten minute time limit.
Once we're succeeded, the event data (called Sonic Adventure: Famitsu) could be downloaded to the player's VMU for use as an exclusive mini game in Sonic Adventure.
But strangely the sequel, Sonic Adventure 2, didn't share the same success.
I wonder what change or part of Sonic Adventure 2 that the Japanese fans didn't like.

Well, I didn't like they dropped the Adventure Fields. To me, Sonic Adventure was like a "Jack of all trades, master of none", while still being a Sonic game at it's core. But Sonic Adventure 2 falls back to serial stages, with only street racing and chao gardens being the only side games.
But that's just my opinion. Maybe Adventure Fields made Sonic Adventure feel more RPGish (even though the game was not), and we all know how much the Japanese love RPGs.
Other than that, despite Hidekazu Yukawa's effort as a Japanese commercial meme, the Dreamcast just wasn't selling as well as the Saturn and Sega was on it's last legs.

I just can't help but feel that post SegaSammy Sega is just not the same as the Sega we grew up with in the '90s.