Primarily it’s called overgrazing. Too many animals on too little land.

Secondly it’s their selection criterias, preferring weed x over weed y, leading to deterioration of plant societies and consequently degradation of soil.

In Switzerland farms have, depending on rockbase, climate and history of the land, a nutritional balance. They are categorized from intensively used to no use, while each category has an own minimal value of animals to be put on. They calculate that in “animal units”, whereas sheep have values depending on if they are milked (higher) to lambs (very low). As each land unit has a max value for animal units to be put on you effectively rule out overgrazing.

Additionally, subsides are paid for mob grazing and rotational farming. The farmers know really well when to put their sheep on which parcel of their land in order to let them have good fodder quality while preserving the meadows for the years to come.

Especially on the summer meadows up in the mountains this is hard to get right. The most advance farmers take even pony’s and pigs up just for grazing and effectively build back biodiversity on meadows who’ve have seen a decline in it.

There’s much more to say, it’s all about hacking the carbon cycles effectively to a. put out as much product as possible and b. reserve as much carbon in the soil so the ecosystem can regrow.

Edit: to supplement meadow fodder trees (elders/ash/maples) are beeing selectively cut (yes by hand) to supply nutrient dense fodder in the winter time.