Why can a field turn into a meadow if a person stops caring for cultivated plants?

This always happens. This can be seen in abandoned villages and abandoned fields. Cultivated plants are very demanding to care for. Only some species can grow on their own without human care, without harvesting fruits and fertilizing the soil. Therefore, the fields begin to overgrow with weeds. Cultivated plants die and only wild plants grow in the fields, which do not need human care. The composition of the soil also changes quite rapidly. But this process is completely reversible and a person can again make a field in that place.