What make TEA18362T by NXP to work upto 75W?
The device is a "\$\color{green}{\text{green-chip}}\$": -


  The TEA18362T is a controller IC for low-cost Switched Mode Power
  Supplies (SMPS). It is intended for flyback topologies. The built-in
  \$\color{green}{\text{GREEN}}\$ functions provide high efficiency at all power levels.


And, if you read this document by Texas Instruments entitled: -

Green-Mode Power by the Milli-Watt


You'll see that there is legislation the suggests different architectures for flyback controllers depending on what power category they are in and, 75 watts is the limit for the low power devices. Hence the TEA18362T is suggesting that it has all the features to meet that legislation/regulation up to that power: -


  The TEA18362T enables low-cost, highly efficient and reliable supplies
  for power requirements up to 75 W to be designed with a minimum number
  of external components.


It doesn't say it can't support designs above 75 watts.