Because you are not. SOME law firms might offer a 30 min chat for free to try to entice you in, but there is no entitlement to anything, any more than there is an entitlement to 30 mins free haircut, or massage, or physiotherapy, or accountancy, or music lesson or ANYTHING!
A good law firm will have a chat about what you want first before you agree to engage them, but that's not the same as free legal advice!
Grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr!