Confusion regarding a clause in the agreement.

Q: Hi, I recently bought a villa and have got the agreement and registration done. However, my query is regarding the "Assignment Charges" clause in the agreement. It says,
The purchaser shall not assign/transfer his/her/their interest under this agreement without the prior written consent of the Seller/Developer. In the event the Seller/Developer provides its consent for assignment of Purchasers' interest in this Agreement, then a transfer fee of 20% of Sale Consideration shall be payable by the purchaser to the Seller/Developer, however it is exempted if the assignment is made within the family members;
My question, once registration is done, why should i take the permission from the developer to sell it? Also, it appears to me that the clause is applicable perpetually and any day I were to sell the property I would have to pay the developer 20% of the sale proceeds.
Is this how every developer writes the agreement? Is there something wrong or am I being apprehensive?