Fatigue is true but don't let that take the focus away from the fact that MANY in this team are out of form or just not good enough.
Rohit - Hasn't played well in IPL for the last 5 years (just poor in T20s these days)
Kohli - Out of form for years (sucked in IPL too)
KL - The new choking master (most disappointing of them all)
Pant - Out of form (hasn't done well in IPL in the last 2 years)
Sky - Out of form
Ishan - It's only 1 game. Performed in IPL last 2 seasons.
Pandya - Out of form / useless without his bowling
Jaddu - In form bat (can't slog well in internationals, bowling is poor as usual - never a good T20 bowler)
Varun C - Did decently considering we bowled 2nd
Bumrah - Out of form but was decent
Bhuvi - LOL he gets carted in IPL
Shami - Unreliable even in IPL (how the heck does he play in XI for T20s)
Thakur - Utility player even though he was bad today (he has the ability to pick wickets in middle overs - can get carted at the death badly - useful lower order bat)
Let's categorize these 13 players in the 2 games.
2 potentially over the hill / out of form players in T20s - Rohit & Kohli
3 out of form players - Sky, Pant & Pandya
1 choker - KL
2 not good enough players - Bhuvi & Shami
1 in form but has never been good in T20s player - Jaddu
That's 9 out of 13 players who have been COMPLETELY useless this World T20
Let's look at the rest.
2 newcomers who played 1 game and flopped - Ishan & Thakur
So 11 out of 13 players have been a flopshow
2 decent performers - Varun & Bumrah
But nothing crazy good too.
So out of 13 players:
11 have flopped
2 did decently
End result - Early exit