For me it’s the other way around. In Check_MK I was constantly writing new custom checks and it was all manual code and overall felt like Nagios on steroids (what it was back then) - just not in a good way.
In Zabbix you can do everything in the UI without messing around in the file system. And things like translating SNMP results to readable text works throughout the system without having to include a Python file and then call it from within your various other checks. All the alerting logic can be clicked together and easily amended in the UI. It’s so much more comfortable once you’ve figured it out.
Google, Bing, and a plethora of others.