I have the suspicion that they really only wanted to test the new textures of the new mythic units from the Age of Mythology Retold.
The other possibility is that they wanted to add a fun twist to Summer in the Northern Hemisphere for Season 5. In the 3rd Season there was also a Sea Monsters event, but neither the Kraken nor Nessi came out (only trophies), so this time to correct themselves, they made Nessi CANON.
Of course, since I was very busy with my concept of Aztecs (Aztecs Civilization Concept for AoEIV_ by GoldenArmorX), and I have one planned for Incas on the way , Mayas and Mapuches, time ran out and I did not have enough hours to enjoy them. I’m trying to play the monster maps as much as possible today so I don’t forget them, and take as many captures from them as possible.
The good thing about Aoe4 is that at least most of the events you can complete in a single day, killing you hours, but in a single day. In Age2 they are still with the mess of the event that forces you to play every day like Dragon City on Facebook.
About the event itself:
The fact that the monsters only spawned on 4 maps limits the possibility of seeing them frequently. That they only appear to give you a boost and then disappear, like it makes them uninteresting. It’s fun to watch them once, but then they’re gone and there’s no joke. If you fought against them it would be something else. The deer in the Enchanted Groove, for example, had the problem that it didn’t give you more meat or anything extra, it was just to get a Banner.
It would be nice if they appear again in some future event, although with stats, as Creeps or as gaia units for the Editor. Or in some future Enchanted Groove “Remaster”, that includes both them and the Enchanted Deer, and that this one also has a bonus or gold tea instead of meat.
PS1: Facebook’s Dragon City expired in 2020, “Rest in peace Dragon City”.
PS2: I miss the Enchanted Groove. It was a fun and cute biome. I hope one day they bring it back officially. I mean, it was “optional”, there was no problem if you didn’t want to play it. Of course, so as not to annoy the ranked people, it would only be available in Skirmishes or custom games.