Both fencers hit, why did the other one get the point?

Because in foil and sabre, hitting isn't enough, you have to have the right to hit. It's called right-of-way (priority): when both lights come on, the referee awards the touch to the fencer who was attacking, and an attack means arm extending, threatening the target, moving forward. If your fencer got hit while the opponent was mid-attack, and answered by just sticking their arm out (a counterattack), the attacker's light wins even though both landed.

Watch the referee's hands after a double light. One arm sweeps toward the fencer who had the attack, that's who earned priority. The most common versions you'll see: the attacker scores over the counterattacker; a fencer who parries (deflects the blade) steals priority and their riposte scores; and if both genuinely attacked at the same instant, it's a 'simultaneous', no point at all.

Épée skips all of this: both hit within 1/25th of a second, both score. That's why a kid switching between weapons can find the rules baffling for a while.

The fix isn't to hit harder or faster, it's to learn to finish an attack when you have priority and to parry first when you don't. Coaches drill exactly this, and it clicks for most kids within a season.