Because it directly affects two parts of the game. Do you choose to build a building or more control and units on the map? All this is not there, engineers at the start are meaningless, they have lost one of their
one of main meaning. Are you bad at command and forgot to reinforce your troops? You have lost the initiative. Now this is not there, all this reminds me of the Activivision initiatives so that it would be "friendlier" for a noob to play instead of understanding the game and improving skills.
I am mentally mostly thinking about the auto reinforce, but let's slightly split the argument.
Regarding autobuilding/teching, I can see a point. However, I think that CoH2 did a very bad job at this mechanic as well. Only 2 out of 5 factions need their engineers for teching, and neither engineer units have a larger impact on the front. Even if you'd need to retreat them at full health, their combat potential is relatively low. While you could obviously get a bit of DPS out of them or try to sweep a mine later on, you can definitely afford to retreat them. Adding to this, the time between building the tech building and acquiring enough fuel to build a vehicle from it is far apart, and there is no benefit from just having the building itself. It does not matter if you build tech as soon as you have enough fuel for it or you accumulate fuel and start building at the last moment, finishing just in time for producing the vehicle. This usually gives you a large time frame (e.g., during which you are almost guaranteed to retreat your engineer. The only instance where this influences timings and the game is getting the 222 out as Ostheer, because the window is rather small with 30 fuel for the 222 and mistimings between BP1-T2-222 can delay it a bit. I never really had issues with the T70 as Soviets. 70 fuel is roughly 3 min worth of income. That is a large enough window that I probably need to retreat my engineers from combat in between anyway. Ostheer T3 and Soviet T4 have even larger windows.
To fix that, engineers would have to be potent in combat so that not having them on the front actually made a dent in your defense and the time frame between teching up and actually getting something useful out of it need to be reduced. But still: Is this really worth and fun, to take so much of your attention away from the battle? People where already complaining about OKW T1 needing to be clicked so often for tech ups that are both necessary, but only worth little. Yes, a good player will time everything correctly, but this is memorizing stuff and has nothing to do with tactical skills, which should be the focus of an RTS.
Regarding the auto reinforcement, I do not see a point. This is mostly memorizing stuff that you'll usually not think about anyway. You will skip over your base, select everything and reinforce >90% of the time anyway. In very few times, there will be some decision to make to tech up or reinforce either squad A or B. But those are rather scarce. Again, is it really worth taking focus and time from real tactical decision making? I personally don't think so. But even if you disagree, your argument "Are you bad at command and forgot to reinforce your troops?" can be used to justify a lot of clicking. (Exaggeration obviously
All your squads fall asleep if they don't get an order for 30 secs, after which you need to press the wake up button and they go through a 10 sec animation before taking commands again. If you're bad at command and forgot to wake up your troops, you have lost the initiative. Which is exactly how you justify manual reinforcement. This example actually comes fairly close to reinforcing. Squad is not combat ready (asleep/not reinforced) -> go to squad, spam button without having to decide anything in 90% of cases (reinforce, wake up) -> do something else for a while -> give order to squad again.
What about auto healing then? This should surely be manual. With a long cool down, it could even include some actual decision making (do I heal the troops now or after the large battle?). The healing automatrons should be very bad for gameplay and differentiating good from bad players if I follow your argument.
And this can be expanded hugely. Refueling tanks, automatic reloading, autotargeting of squads. Your main differentiator is who can remember and click things faster than the other player, not who is actually able to pull of the better assault.