The availability, the limited sizes, the weaker system. Everything about them are substandard to a good Weaver/picatinny/integral rail system.
But being open minded I'm interested to hear why they might be superior.
No one said they were superior. When used on a rimfire as they should be used, there's no reason to say they are junk, insufficiently strong or reliable, or substandard -- unless that view were unalterably held.
Except for variation in dovetail dimensions between some 452 models, the 11mm CZ dovetails are no different from other European .22 rimfire rifle makers in how they function. There may have slight differences in dimensions from one make of rifle to another, but dovetail grooves are quite effective in mounting sights. The minimal recoil in rimfire rifles doesn't require the weaver/picatinny system's ability to withstand high levels of recoil. International Olympic-style shooters find no issue with using the 11mm dovetail grooves on their rifles when mounting their sights, including biathlon competitors who put their rifles through more rigorous use. The reason many European rifles have dovetails only is because they are more than sufficiently solid and reliable. Shooters of European rifles that aren't D&T'd for bases are able to use the dovetails for scope mounting without concern for dependability -- with the provision, of course, that the correct type of dovetail rings are used.
Many CZ shooters, especially those using 452's, may experience problems when they don't get the correct size dovetail rings as some 452 models have 3/8" grooves instead of 11mm. Many North American made .22 rimfires have 3/8" dovetail grooves. There are rings for 3/8" grooves and there are rings for 11mm grooves. These are often not interchangeable. But there are rings that work effectively on either one, with a reversible clamp plate or a design that easily works on both, such as BKL.
Many North American shooters are more accustomed to weaver/picatinny style rings and bases as a result of centerfire shooting. As a result, many North American .22 rimfire rifles come with bases or rails. The rails are available with elevated cant to allow for shooting at further distances with .22LR; elevation adjustable dovetails are available but these have more moving parts and as a result may be considered less reliable.
The long and short of it is that dovetails can be used with complete confidence to mount scopes on a .22 rimfire rifle. It's necessary, however, to use the correct size rings, and to avoid cheap rings, just as anyone should avoid cheap weaver style rings.