Because it is these professional repairers lobbying for the laws.

This sort of thing always aims to get the law to identify some kind of professional certification needed to qualify, and then that certification gets more expensive and limited (eg. by saying studying a specific course is needed, but only X thousand places are offered per year).

Eventually, people who have done that course and qualification get so expensive that that becomes their only job, and you won't find a handyman-type person qualified to do those tasks.