Because even to this day, Starcraft 2 has the best hotkey customization, the best quality of life options and the best RTS gameplay from a technical standpoint.
You can change ANY hotkey you want. The attack hotkey, the stop hotkey, patrol, (Aoe4 doesn’t have patrol) hold position. You have camera hotkeys. Aoe4 doesn’t have camera hotkeys. Take a look at this hotkey setup, which is impossible in any game, but its possible in SC2.
You can easily switch to this keyboard setup even after playing years with the standard RTS or grid setup and you will be able to use twice the amount of control groups without having to stretch your fingers as much as in the standart hotkey setup.
The hotkey customization Aoe4 offers is not just worse than SC2. Its worse than Aoe2 DE and Aoe3 DE aswell. Its unacceptable.
You can set your own preferred colour and display it ingame and even change the colour of your enemy. Want to play violet against orange? You can do it! It sounds simple yet I don’t know any RTS which offers this customization.
Starcraft 2 has the best replay-viewing and casting UI. The current UI from Aoe4 is obviously inspired by Starcraft 2 UI, but its still not on par and missing a lot of features which SC2 has for many years.
Individual unit control is terrible in Aoe4. However in SC2, you can easily select hurt units by clicking on their portrait in your selection. You can select hundreds of units at once and one tab will show you up to 50 units. Their icons will change when damaged, so one click on the icon is enough to pull back hurt units - simple but extremely effective micro tasks are made easy. You can’t do this in Aoe4 at all, instead you have to find hurt units with your cursor, select them manually and pull them back.
Aoe4 does not support automated tournaments. SC2 does.
Aoe4 allows you to view the map before selecting your civ, which is a terrible idea and has a big impact on balance since players will tend to choose civilisation depending on the map instead of being able to play what they want.
Aoe4 does not have civilisation-specific mmr. SC2 does.
Aoe4 doesn’t even allow you to view the fully revealed map after the game. In Sc2, not only is the map fully revealed when the game ends, you can immediately open up the replay and play back the game to see what you or your opponent did. Aoe4 didn’t even have the option to view replays in the stress test. Thats one of the most important parts of any RTS.
Aoe4 offered no player profile, no statistics for maps, cvilisations, matchups. No chat with other players in the game browser. No channels for strategies, no clans.
There is probably a bunch of other stuff, but long story short, SC2 is the most developed RTS on the market more than 10 years after its release. You would think an RTS released in 2021 would build upon this foundation and improve it, but right now Aoe4 has less features than Starcraft 2. And Starcraft 2 is free to play nowadays.