Why do some governments make car insurance mandatory? Is it just to gain more money?

According to me,

Car insurance should always be mandatory for car owners, not just to safe guard his own car from aaccident or theft, but to secure Third party interest also. 

Dude, I don't think you understand what insurance is for. There are many private insurance companies, and the state has nothing to do with it. First of all, the driver needs insurance to get help in an emergency. I constantly look at various reviews like maserati ghibli insurance cost because I'm really curious about how different insurance companies work.

Not only to gain money but also to protect the car's owners from the third party liability that may arises at any time during the course of insurance , as by insurance of T.P, being mandatory the government guarantee the compensation and indemnity to the third party in whatever the financial position of the insured at the time of the accident or when the event take place. i.e The mandatory insurance objective is to guarantee compensation and indemnity to the third party when liability arises upon the insured .

Thanking you

Governments do not make car insurance mandatory they rather make the liability of the car driving mandatory and that is why we find the completion on TPL alone 

Car insurance helps society in many ways, for example, when there is a car accident, one of the two people involved will burden the loss and pays for both cars damages, thus, lives in lower standards for an extended period after the accident. Add to that, if the damaged car is luxurious and expensive, the other driver is injured severely, there is public property involved, all these elements cost a lot of money to repair. Having insurance will eliminate the loss (not the accident).