CET was introduced by the Germans in 1940. The actual time here is GMT + 10-20 minutes.
For obvious reasons that kind of time can never be used. It would mean that while in Ostende it is 4:00 PM, in Brussels it would be 4:07 PM and at the same time in Arlon it would be 4:12 PM give or take a few minutes. In our modern world this would be extremely confusing and totally unpractical which is why time is rounded up to the hour, everywhere.
Also GMT here in Belgium would be a problem. Right now in June the sun sets at about 10 PM, if we stop using summer time and stay on winter time all year round it means the sun will set in June at 9 PM but if we start using GMT it means the sun will set at 8 PM in June. Only vampires could be happy about that
And to make things worse right now in June the sun rises at around 4:30 AM, if we stay on winter time it means the sun will rise at 3:30 AM and if we move to GMT the sun will start rising in June at 2:30 AM... See how this would make GMT not the best choice over here? 2:30 AM is not a time to have the sun rising over here, in my opinion.