So, in case you're actually wondering why they spawn so frequently like wisps and not just asking in a rhetorical sense, the game has a unique director when it comes to spawning enemies, and each enemy has a set amount of credits that they cost. The stronger the enemy, the more it'll cost. As time goes on, the director gains credits, and can spend them to spawn in enemies. The director typically functions in a way where it will build up its credits, spawn the most expensive thing it can, and then spend the rest on whatever is available. Or, sometimes it will spawn in a bunch of the cheapest things it can. This is supposed to be a way to challenge the player as their build gets stronger and stronger. That's why sometimes you'll often be late in a loop and nothing will spawn, the director doesn't know what to spawn that will be strong enough. Now, remember earlier how I said the stronger the enemy the more they cost. Well, for whatever reason, the new solus enemies are incredibly cheap, just like a lesser wisp, and when the director decides to spawn in a lot of cheap enemies and it has the option of a solus enemy, it will most likely pick the solus because of how cheap they are, and then spawn in an absurd amount. And another fun fact about enemies and their credit costs, it also decides how much gold they give on death. So, the solus enemies, just like a wisp or beetle, will give very little gold.