I have a few years experience with MREs admittedly some decades ago, between the two gulf wars.
1) On a short term subjective individual basis anything mom didn't put in your lunch will be defined as awful, such that if you swap lunches with the kid next to you in grade school you'll hear plenty of complaining about lunch is inedible, even if every individual loves their own mom's cooking. This goes away after some weeks.
2) Most eating is about social signaling, virtue signaling, conspicuous consumption. So the stereotypical "first day pass" every new private passes up an objectively better free meal at the DFAC for an icky greasy chezburger at the on post Burger King and claim its the best food they've ever eaten. Likewise in the field you're issued an MRE that tastes pretty good and you'll hate the lack of choice no matter how good it tastes; offer soldiers their choice of cardboard flavored instant Ramen and they'll declare that a culinary masterpiece. Imagine the reaction if a Michelin Star restaurant refused any serving choices at all; here's your drink and meal chosen by us; no matter how good the food is, the complaints would be deafening.
3) Sometimes the food is objectively bad in taste or texture or consistency from pack to pack. The famous vegetable omelette can be delicious or randomly they include too much soggy woodchip-like "mystery fiber" and thats just disgusting although I generally like that MRE. Also the Italian sausage MRE sandwich, which has been around at least a decade and is essentially a rolled up pizza, gives me and every other soldier I've asked, heartburn, and essentially no other food gives me heartburn (whiskey shots, but only sometimes). On the other hand we had a running joke / research project in my platoon along the lines of the army counts every meatball in the spaghetti entree, expect a hand receipt for nine serial numbered meatballs with every entree, or whatever.
4) Sometimes the system is subjectively inconsistent across the system. Almost everyone in the army ate a chef boyardee ravioli or spaghetti with meatballs or salisbury steak meal when they were kids, and the army has produced MREs that are consistently indistinguishable from the kid dining experience to the point of generating homesickness. MREs contain (used to contain) a poundcake that was indistinguishable from an flat unstuffed twinkie. And of course a pack of M&Ms for desert is literally a civilian pack of M&Ms making it very consistent with civilian life and everyone likes those. On the other hand, something like the famous omelette is very binary, almost political, in that about half of soldiers will trade it for anything and refuse to eat it, and the other half think its pretty tasty when warmed up. I have no idea what the army was thinking shipping something half the troops will hate.
5) If your chain of command suck or for whatever other reason your morale is low, its totally socially acceptable in the Army to complain about the food. Yet going the other way if field conditions are so rough you'd eat anything "SERE course style" then lack of complaining also worries leadership. Basically leadership operates under the model that if the worst thing the troops are doing is complaining about the food, then the leadership is probably doing mostly well.
I suspect in the long run once the PR dies down the pizza MRE will be hated by the troops because everyone has their own ideal mental model of a pizza and "one size fits all" isn't going to work for anything thats not a mass produced kid food (like chef boyardee ravioli). Also if its essentially an unrolled italian sausage MRE sandwich, almost everyone is gonna get heartburn.