I think if it helps stop plonkers touching gas who haven't resat their certificates, then it surely increases your business and incomings if you do resit them. So it's just a case of getting it done and out of the way each 5 years. And keeping clued up during the 4 and a half you're not thinking about it......?
I guess the aim is, to stop people messing with your job. The one you're really skilled in doing. And can't balls up.
So I can see the reasoning in doing it. Be thankful it's not annual. We have some sparkys from America in some states that have to reapply for their 'license' each year. A bit like our taxi system. And some people don't get it renewed when the cap has been hit.
Thank god it's not over-regulated like that! Imagine building a business up, and customers, only to then need to get your competitor in to sign it all off!!!!
That'd annoy you! And it'd be open to abuse and fixing and brown paper bag payments and whatnot.