Sports games and people who buy them are popular targets for a lot of reasons.
The primary reason is not so much that the games don't ever change, but that they don't change signifigantly.
I'm a big defender of JRPGs with classic mechanics, and heck RPGs in general. I defend turn based combat and similar things, with an attitude that "if it's not broke, don't fix it". Despite this the thing is that with sports games there are rarely any real innovations, or changes, RPGs at least have differant storylines and weapons and such, along with their few unique tweaks to gameplay. Sports games don't usually include any signifigant gameplay upgrades that couldn't be patched in except maybe every two or three years. Generally speaking they charge people for little more than roster updates and a new number of the front. The graphics and technology rarely change signifigantly within a console generation as they run on the same hardware.
Sports games are also insturmental in helping to bring the lowest human denominator into the hobby. While not only dumb people like sports, sports are something that dumb people can and do appreciate. "guy who can jump high" is something any mouth breather can get their brain around. Sports franchises brought these people into gaming by the millions when they got to this level of technology. Given the sheer number of these people involved in gaming you saw a lot of effort shifted away from producing serious games, towards catering to this crowd. What's more with this audience already there for the sports games, it helped direct the trend towards producing other very simple "by the numbers" games specifically for the lowest human denominator.
The money spent recycling the same shooters, and buying pro-sports liscencing rights are things that could be being used to produce serious games, for serious gamers. However there is more money to be made here, so that's where a lot of the effort goes. There is a lot of resentment over the simple fact that someone who is a "serious" gamer will have to wait months for titles while they release things like "Call Of Duty" and "Madden" since those titles will sell millions of copies.
What's more the ease of producing games like this, since your dealing with minor updates to an existing formula or engine, has influanced the industry to the point where it prefers to be able to cater to the areas that take the most minimal amounts of effort. Simply put you only really need one game for each sport for a given console generation, everything else is just going to be tweaks on that formula since the hardware won't change. With shooters they tend to be built right out of kits, things like "Havoc Physix", "Unreal", "Graw". Shooters don't have the same basic controls because of some design standardization developers agreed on, but because the guys who developed the actual engines set them that way, and they all use the same engine. The meat of game design is on producing graphics and tweaking an engine someone else produced again and again. This came about due to the easy to please, mainstream who want games about "men who can jump high" and to watch pretty explosions while they tap a button.
Sorry if this isn't terribly polite, but you wanted an honest answer as to why this attitude exists, and this is what I think. There are people who are smart who like sports (plenty of them) and plenty of people who can enjoy mainstream games, and more serious ones, do nobody should think I am nessicarly dismissing them. In the end though there are far more people as customers for gaming out there that can't really appreciate games beyond this level, than serious gamers and those who like to play on both levels.
When you understand the thought processes involved, even if most people don't (or can't) articulate them, it's easy to understand why discussions on this subject can get so nasty.
I'd immediatly guess that while both have defended casual gamers to some extent (being professional) in the end Yahtzee and Bob are serious gamers are their core, and also very picky ones, which is why they are critics. I don't know if they would agree with what I've said, especially in the course of their professional productions, but I'd imagine both have some resentment towards the simple fact that we get so much of this stuff shoveled on the market in lieu of other products. It's sort of like the gaming equivilent of how Bob complains about Michael Bay movies and their mainstream success due to who they appeal to, as opposed to genuinely good film making.
