Well apart from the humongous amount of work laminating and cutting each individual card would be compared to just sleeving (even assuming that you don't overheat or cut through a card in the process and that your are steady enough to cut all the cards at the exact same size, which usually requires specialized equipment), lamination is not considered a safe
conservation technique. The laminating process itself (heat + pressure and/or adhesive) is not safe for documents. Most laminating materials are not made for archival and can be chemically unstable. Moreover, cold or heat lamination in most cases cannot be reversed, which is quite a big deal in the case of old OOP cards or precious documents.
I've actually tried to use laminated printed HQ cards before I was able to score a few copies of the game in thrift stores and that was mostly a pain. I would never try to do this with original cards. Laminating the cards themselves usually introduced bubbles at some point and the texture would be different depending on heat. Any dust particle or hair left on the cards before laminating stood out quite a bit when examining the finished product. I tried both leaving a border around the cards (non-sticking hot laminate) and cutting to size (cold or adhesive hot laminate) but in the first case getting a consistent size between cards was a challenge and in the second I would usually have the laminate lift from the cards in some areas. In both cases, the cards were usually too thick, too rigid and weird to handle and shuffling would eventually ruin the borders or lift the laminate from the cards. And most non-professional round corners cutters cannot cut throught laminate cleanly and reliably so you would have to keep the corners square and those can be ruined quite fast. After a few tries I simply abandoned as there was no way I could reliably and cheaply reproduce a HQ set of cards matching my expectations.
Sleeves are easy to use and cheap if you don't go overboard and get the most expensive ones, if they break you simply slide the card in another one, most of them are acid-free / archival quality, soft or rigid depending on the thickness you choose and they do not hamper shuffling. And they do not modify the cards in any non-reversible way. Some people hate sleeves as they interfere with the tactile pleasure of playing cards and when they are new they tend to slide around the table and getting a stable stack is a challenge but to be able to preserve HQ cards just a bit longer I can deal with those few problems.
Edit : replaced lamination with
conservation, which makes much more sense
