MED1/ MED2 non-qualifying treatment

What is the rationale/ logic behind routine treatments not qualifying for tax relief under these schemes?
Things like contact lenses aren't covered, but laser eye surgery is.
Crowns and orthodontics are but false teeth and fillings aren't.
I know that some of these are already covered by PRSI, but as far as I know only 30% of your dental treatment is covered (e.g. €30 of a €75-90 filling charge).
To me it seems like penalising those who can't afford the more expensive option? Who wouldn't prefer a crown than false teeth or laser eye surgery than contact lenses, but can't afford it?
Just curious.

I presume it's to do with the frequency of a possible claim - laser eye surgery is a once-off treatment (or at least it should be!), whereas contact lenses are ongoing treatments. Same with the serious dental work vs routine dental work.