Hotels refuse to issue invoice when it is booked and paid thru an Online Travel Agency or third party

Every time I book and pay for a hotel through Booking.com or Agoda, I request an official invoice from the hotel. In 100% of cases, the hotel refuses to issue one. This situation irritates me so much that I often have to resort to threatening the hotel with filing a direct complaint with their RDO. Only then, reluctantly, do they issue the invoice.

Hotels often claim that because I did not pay them directly, they are not obligated to issue an invoice. Instead, they tell me to request an invoice from the third-party platform. However, third-party platforms like Booking.com, especially those based overseas, can typically only provide an acknowledgment receipt—not an official tax invoice.

I don’t understand why hotels refuse to issue invoices. Is this some kind of technique to avoid paying the proper taxes? After all, I pay through Booking.com, and Booking.com eventually remits the payment to the hotel.