They are just copying IPL. One of the most exciting part of IPL is a team can play at most 4 international players in a team. Which gives it an international feel. It makes it popular in the countries of the players participating as well becomes more thrilling to local users.
The exciting part of IPL according to me is the level of competition and the quality of players and they should increase the number of foreign players in a team for the real excitement but they have their restrictions and we assume that they are doing that to help the domestic players and it is a good thing as it is giving them a financial boost as well.
You cannot call other tournaments copying IPL, club matches are not a new concept and Soccer is more popular in the club circuit than International matches other than World Cup and Cricket is just trying to replicate that in the T20 format.