Most of this game's drawing comes from draw supporters, primarily Professor Oak's New Theory, Professor Juniper, N, and to a lesser extent Cheren, Sage, and Bianca, and Pokegear is used to fetch them. Now Pokegear sometimes whiffs and that's quite annoying.
In addition, people (used to) use Pokemon Collector to get their Basics out as soon as possible. However, that card usually conflicts with Random Receiver, because when you use that you are usually looking for something to get a new hand with (PONT, Juniper, N), and you don't want to run into Collector. So by replacing Collector with the "Ball" Trainers (mostly Dual Ball and Level Ball), Random Receiver increases in effectiveness, because you're guaranteed to hit a hand refresher with it.
The "ball engine" existed before Random Receiver, as people realized the game is just too fast to use Collector - you usually want to get out Basics AND draw through your deck at the same time. Dual Ball + Level Ball is particularly effective in Eelektrik decks because the main target that you want to bench a lot of (Tynamo) is searchable by both of these balls. Ultra Ball is just icing on the cake since it can get Lightning in the discard. Celebi decks have always preferred Dual Ball because it needs so few Basics out at the same time (just Celebi + an attacker, really).
tl;dr using a draw supporter + finding basics > just finding basics