Prakash Shah Cabbage is going to flower. Two possible reasons:

1) for several weeks temperature was low enough for vernalization of cabbage plants . For example see:

Effect of effective accumulated temperature of vernalization on vernalization related substances of cabbage. (cabdirect.org)

https://repository.up.ac.za/bitstream/handle/2263/53542/Ngwenya_Effect_2016.pdf?sequence=1

2) some genotypes of early cabbage turn to flowering after complex stresses at higher temperature than usual.

Thank you professor @Alex Ignatov

This may have been a result of hormonal/metabolite imbalance brought mainly due to stress e.g., above normal temperature.

Thank you dear professor @Aaron Siyunda

Possibly mlo

Because of abnormal climatic conditions