Why can't they just make games that are both mobile and PC accessible? Just like Roblox. It's one of the reasons Roblox is hugely successful, because it's accessible for both PC and mobile players.
Because they were handled by different team at SEGA,
some are good at console (Sonic Team, RGG Studio, Creative Assembly, Sports Interactive, Relic Entertainment, Amplitude Studios),
some are good at arcade (Division 5 including AM2 and SEGA Music Team, Sega Studios Shanghai, SAI)
and some are good at mobile (Sega Networks, HARDLight, PlayHeart, Sega Sapporo Studio ).
Also outside from Sonic, FM, and Miku,
I think SEGA weren't interested in mobile games for global version that much.
SEGA's mobile games mostly sold well only in Japan,
Chain Chronicles is the example.
It was huge in Japan but kinda flop in global version.
Even last month only 1 global game managed to the SEGA's top 12,
others are Japan only games.