In 1.17.1, flowers used to generate splotches of 1 random flower and sometimes tulips.

In 1.18, flowers generate all kinds of flowers in one splotch (also unbalanced, because it generates 10 or even more dandelions and only up to 5 cornflowers, f.e.)
Tulips are now much more rare.

The issue is not only in plains biomes; in other biomes (f.e. taiga, savanna, etc.), where only poppies and dandelions generate, they are also mixed rather than only 1 kind of flower in a splotch.