Defi is not really vulnerable to attack, it is only due to the subjectivity of Defi projects about security, then they are only interested in the amount they have raised but are sketchy in the security mechanism. they took too much importance in developing the protocol, and that in turn made it easier for hackers to attack.
This is also one of the problems that makes Defi not a long term trend. As it may be sold off at any time, people should not hold or staking at this time.