What affects how many quick attacks are needed to fill a charged attack? [duplicate]

Every move in the game has an energyDelta. This figure represents how much energy you gain (or lose) from using the move. Fast moves has a positive delta, meaning that using them gives you energy. Charge moves have a negative delta, meaning that using them consumes this energy.

In other words, if you have a fast move that had a high energy delta (like Lock-On) and a charge move that didn't cost much energy to use (like Tri Attack) then you could use charge moves in very rapid succession. On the other hand, if your Pokémon had, for example, Hidden Power as its fast move and Hyper Beam as its charge move, it would take much longer to get enough energy to actually use your charge move.

As evolving a Pokémon will give it an entirely new set of moves, your Porygon likely went from having two very energy-efficient moves to having two fairly demanding ones. This isn't necessarily always a bad thing, as those moves typically deal a lot more damage than the faster ones, but there's a lot of factors at play when deciding what moves you want on a specific Pokémon.