Why were the Cossacks the instigator and the most active participant in the popular movements of the second

Why were the Cossacks the instigator and the most active participant in the popular movements of the second half of the 17th century – the first quarter of the 18th century?

The free Cossacks were often dissatisfied with the encroachment of the tsarist power on their legitimate Cossack privileges, which consisted in self-government and the possession of vast land plots rich in fish and game. When the tsarist administration tried to demand the extradition of fugitive peasants from the Don, the Cossacks immediately raised an uprising led by S. Razin. Also, the Cossacks were outraged by the policy of Peter 1, who took away their profitable salt sources and intervened in internal affairs, which led to a decisive speech by K. Bulavin.