<div>Why doesn’t the cronjon start automatically after I rebooted the server?</div>

Hi
Why doesn’t the cronjon start automatically after I rebooted the server? I always have to do this manually.
All crons are entered in the crontab file. We have 100 Magento shops. I then have to toast manually for everyone
If I start php bin/magento cron: run at the same time or one after the other for all 100 shops, it affects the server’s performance for a long time.

Thanks a lot.