Another reason behind the shift of cricketers to the T20 format is that most of the county leagues in the T20 format include Big Bash, IPL, PSL, BPL, Caribbean League, SA_20, and dozens of other leagues, resulting in a constant demand for players in the T20 format. That is why most of the players retire from ODI format and Test format but do not retire easily from T20 format.
Yeah that can be one of the reason but not many T20 players can play test cricket. Test cricket needs a lot of patience, stamina and skills. The same can be talked for 50 over cricket, whereas in T20 it is a matter of few overs. When players retire they continue to play T20 as it doesn't need them to be on ground a full day. They only need to be on the ground for a few hours which their bodies can adapt to easily.
No one having doubt about beauty of the test format, but recently we have good changes with the help of T20I and bazball bring significant changes and its beauty is going to be at his best even many are feeling it is not real cricket but no one can stop these changes and these were needed as well now aggression and politeness both are doing good job, and we have good entertaining stuff like we have in third test match of India vs England series hopefully youths will be delivered like we have from Jaiswal and Gill will be also having good performance in coming matches, but they need to be in touch because skipping this format is surely not good deal for all fans and cricketers need to be had good things in this game after very long bore era IPL bring historic changes and things are now at new level.