I can understand why PCGS and others may have difficulties in adapting a slabbing system to medals.
Medals can vary greatly in diameter, height of relief and thickness, and if a collector wants all of his medals slabbed to a standard slab size, there will be inevitable and unavoidable problems.
Ancient coins also present a range of problems for slabbing, although high end ancient coins tend to be auctioned in slabs in more recent times.
Perhaps a slabbing system can be devised to accommodate most medals and not just a few, but that will depend on commercial viability.
Pristine condition medals like coins, need protection.
The answer in how a medal is be protected cannot always be found in slabbing.
The way a medal is designed is not constrained by the needs of circulation, and is more an expression of art. Partly because of this, museums always display medals unslabbed, so that that they can be better appreciated by the visitor and that attitude appeals to my way of thinking.