Motion inputs aren't arbitrarily difficult. They're intrinsically tied to the game's balance. Basic special uppercut moves like the Shoryuken use the forward->down->downforward motion to ensure the player cannot hold back to block during the motion. The player must commit to use their strong special uppercut move frames before they've actually unleashed it. Guile's Sonic Boom projectile requires the player to "charge" the move by holding back for a couple of seconds before being able to unleash it. This creates a risk factor, since the opponent is then incentivized to cross up Guile to make him lose his charge. However, this is where Guile's special uppercut, the Flash Kick, comes into play. The Flash Kick can be simultaneously charged along with the Sonic Boom, to disincentivize the opponent from attempting to jump over Guile. Mapping any of these moves to a single button press is a balancing nightmare. Street Fighter 6 has a "Modern" controls option that does exactly this, and it comes at the cost of a big chunk of the character's available movelist. Even with that huge tradeoff, the Modern versions of several characters are still considered high tier. Even then, you hardly see any Modern control players in the upper echelons of Ranked matchmaking because, ultimately, it's way easier to learn the motion inputs than it is to have a solid gameplan.