Corners curling towards the goal have displaced the outswinger as the default at a large number of clubs. The shift follows from what an inswinging ball does to defenders and goalkeepers.
Any contact becomes a shot
A ball already travelling towards goal only needs to be touched. A flick, a shoulder or a deflection off a defender continues on the same path.
An outswinger moves away from goal, so an attacker must generate the entire change of direction himself, which requires a clean and powerful header.
That difference means the inswinger converts far more of its contacts into threats, including the accidental ones nobody planned for.
The goalkeeper is forced to decide
A ball curling towards the net cannot be ignored, so the keeper must either come to claim it or hold his line and hope it is dealt with.
Coming means moving through a crowded six-yard area with players blocking the route, and holding means watching a ball drop towards his own goal.
Both choices carry risk, and the goals conceded from these deliveries frequently come from a keeper who started to move and then stopped.
Defenders are running towards their own goal
Clearing an inswinger means heading it backwards over your own head or turning to attack it while retreating, both of which are awkward under pressure.
The defender's momentum is towards his own net, so a mistimed contact travels the wrong way rather than safely upfield.
Own goals and deflected finishes from corners are overwhelmingly produced by this delivery for exactly that reason.
What changed to make it viable
Inswingers depend on a taker who can curl the ball consistently with the correct foot, which historically limited the option to whichever side matched the available player.
Squads now routinely carry left and right-footed set-piece takers specifically so that both corners can be delivered inswinging.
Improved ball flight and the emphasis on rehearsed routines also raised the value of a delivery whose path is highly repeatable.
Why the outswinger survives
An outswinger takes the ball away from the goalkeeper entirely, which suits teams whose plan is a clean header from an attacking runner meeting the ball at pace.
It is also safer against a dominant keeper, since the delivery never enters the zone he is entitled to claim.
Most teams now use both, choosing by opponent, and the choice reveals whether they intend to attack the keeper or avoid him.