Those people don’t boycott the game,
they are rather very skeptical for the concept AoE4 does try to do.
We just don’t see such games to succeed,
it’s not like people are boycotting the E-Sports RTS genre,
the developers are just presenting games people have no interest into.
For example recent Kickstarter for
Sparta Definitive Edition: / KINGS AND SOLDIERS: Ancient Warfare failed.
Its pretty much like AoE sequel in 3D for AoE1.
They wanted on Kickstarter just 33.400 dollar to make the game. And failed to raise this money. The game has free beta/demo, you can check it, its pretty decent.