That volume is a double-edged sword for collectors there are hundreds of distinct Japanese Pikachu cards in circulation, which means knowing which ones actually hold value (and which are $2 bulk) is harder than for any other Pokemon
Combine this with Skarmory, Drampa, or even Oricorio, and you have a deck that can take on anything as long as it doesn't brick for extended periods of time
For example, in the Sword & Shield sets which were released from 2020-2023 cards featured a similar type-based pattern to the Scarlet & Violet sets, albeit with a striped pattern of chevrons that each contained the Pokemons type symbol
Threatening Roar is particularly effective when your opponent has limited means of bypassing your monsters without attacking, but Frogs excel at utilizing Caius the Shadow Monarch, Raiza the Storm Monarch, and Dark Dust Spirit, which can diminish the effectiveness of Threatening Roar
It all just has to do with demand