Not for want/lack of trying
Definition 1 of 1
Pro Tip 1/3Effort Acknowledged
Indicates that failure wasn't due to a lack of effort or dedication on someone's part. 
She didn't win the competition, but it wasn't for lack of trying.
Pro Tip 2/3Subtle Encouragement
Can subtly encourage or console someone after an unsuccessful attempt. 
I know you didn't pass this time, but it wasn't for want of trying.
Pro Tip 3/3Context Sensitive
Best understood in contexts involving attempts at achieving difficult tasks or goals. 
The summit was unreachable due to weather, not for lack of trying.