Piper Seneca which belongs to my company has limited MTOW = 1999 kg
The reason is because the Seneca owner, or previous owner, was smart enough to purchase and install an FAA STC to decrease the MCTOW below 2000 Kg. This in order to
avoid paying expensive Eurocontrol navigation fees. Note that the STC is merely a placard instructing to limit the payload weight, and not exceed certain weight values. If you really think that you do not pay enough landing fees (yes landing fees will also increase) and that you want to give even more to Eurocontrol and other European bureaucrats, then, go ahead and have the STC removed by your MRO. But you could pay up to 50 eurocents per NM of flight
Of course if you operate outside Europe this does not apply.