Why should there be such an option? ISPConfig restarts services automatically when required to apply config changes. And when you are doing config changes manually on the shell, then you don't need a restart option in the panel anyway as you are already on the shell.
along with what Till said, if you install monit on your servers, and configure the url/user/pass properly in ispconfig system tab - system menu - server config - selected server. then you can see the state of those services in the ispconfig control panel, monitor tab - select server in 'server to monitor' dropdown and click on 'show monit' in the server state menu. clicking on each service will give more details along with options to stop/start/restart each service or disable monitoring.
But monit is not installed by default. I think that in the same section of Status of Services could be added in a column to restart the service. Why do I need this? Because when I'm modifying through FTP and not through SSH, I need to restart without having to access the ssh. Also very soon with the PHP 7.4 entry https://stitcher.io/blog/new-in-php-74 and the cache compilation would be necessary as well. In short this is not mandatory, but it is an additional that really does not bother and can help those who are not accustomed to using SSH. In addition a panel is for that, to have to use the least possible SSH.
While modifying server config by ftp is a very uncommon use case (I've never heard of anyone trying to admin a server via ftp before), there are other use cases that seem more useful in general, eg. maybe restarting mail services when delivery has stopped for some reason .. could be you have a phone with web access but no ssh to properly troubleshoot, so a quick restart would get things going again.
Yes, I make changes to my website through FTP when I don't use github(I know it's not the best way), and I also need restart FPM or Apache to clear the OPcache cache or any other system the cache.
