@Roshan Tiwari
It’s a licensing thing I suspect. They have to pay for bonds and insurance and all of their subs do too. If you pull it and act as gc they do the work and as a homeowner you’re allowed to do your own work as long as it’s up to code.
From an insurance stand point you should make sure that they have insurance (general liability) and probably workers comp - although by the sound of this, this is a smaller contractor who likely doesn’t have it. If one of his subs gets hurt on the job, you’re not at fault, his workers comp should cover that (the mail through the foot example comes to mind).
Lastly and this is IMPORTANT you should get them to give you a certificate of insurance naming you as an additional insured BEFORE they start. As many here can attest, if things start to go south with a contractor, they go south quickly and if a claim is brewing, they will likely cut ties and you’re left holding the bag. By getting the insurance info before that start, you can make a claim against their insurance should you need to (if they accidentally started a fire or something if that nature and it becomes a he said/she said sort of thing.)
Hopefully this helps.
Let me know if you have any other questions,
Andrew