Pay for a recurring service via a one-off payment? What could go wrong?!
Aside from that, a TV license is £157 a year. Let's say a TV lasts three years (which feels conservative, pretty sure I had my last TV for eight), you'd need to get the buyer to pay an extra £471 when they purchase their TV. How is front-loading such a payment in the interests of the viewer? Not to mention you don't have to pay the fee if you're only watching streaming services like Netflix.