How dose match-making work.

My question Is how dose the match-making work? I was play a lot keltullis deck that gave me pro-rank I was last 1-2 days trying shieldwall deck.

After playing I realize the thing Is while I play shieldwall deck for example I play a lot vs swarm decks like rly a lot 80-90% are swarms.

But when I play keltullis Its give me 50-60% time control decks and I dont understand It my keltulis deck Is my own I dont copy decks from internet why dose this system work like that? If Its look on my deck then choice for me enemy who have a lot controls while playing shields the system give me swarms,like this system itself try counter my decks.Im play just 1,5 months gwent and before I was thinking the system look just for my mmr but now I realize Its not only mmr its also "look" on my deck and try match-making me vs harders decks who naturally counter my decks.

The question Is why Is like that? whats the point of mmr If the system also try match-making my deck itself.

Yes my english suck dont need remaind me.