Football goes in cycles. You can't be favourite every year or 50/50. Some years you are just not as good.
I remember back in 2013,when we lost 7-0 to Bayern in aggregate,my father told me "Every great time had a cycle.Barcelona's cycle is over".
And back then it seemed like a decent possibility. The core was getting old and Messi was getting a few injuries,he seemed to start to slow down back then.
Although the past 7 years could have been a LOT better(especially considering Madrid won 4 CLs in 5 years), we should be fortunate that we at least managed to win 1 CL and 4 La Ligas in this timeframe and that Messi continued to be really close to his absolute best.