According to
http://www.esportsearnings.com/players/fighting-game-players, Sonic Fox has earned
$303,846.80 since 2013, which is almost $100,000 a year (and that doesn't even take into account other sources of income such as sponsorships, Twitch subscribers, etc). That means while other players have to contend with "real life", Sonic and other top tournament players can literally make a living playing video games all day. They have access to the best training partners, they don't have to have day jobs (though I'm sure some still do), they almost definitely have the support of their families. Basically, the odds are stacked against the "average" players who
do have to work 40+ hours per week, whose parents don't take them seriously, and who don't have access to other top players as sparring partners. When people talk about "pro" gamers, this is what they mean: Sonic literally plays this game to make a living.
Tack all that onto his natural skill, which is how he got to this level in the first place, and it's no wonder that he can rarely be touched.