The Prophet (صلى الله عليه و سلم) gives this away when he narrates: “Allah (سبحانه وتعالى) made the night short so you can pray, and the day short so you can fast.”
Think about it! Have you ever fasted those long, hot summer days–-days that are a shadow of the Day of Resurrection? Sure you have! But what about praying Tahajjud, when the night lasts only 3-4 hours? That’s easy! You don’t even have to sleep and wake up, you can even stay up a couple of hours and enter the blessed last third of the night, when Ar-Rahman (سبحانه وتعالى) descends!
But try praying Qiyam the long, cold winter nights. It’s tough–Isha is at 6pm. By the time you get home, eat, relax, etc. it’s already almost 11pm or midnight; try waking up early and you can’t! But how about fasting the short winter days, when the fast lasts only 8-9 hours? Easy! (Getting up a bit earlier to pray Tahajjud before Fajr is easy, too!)
So fast the short winter days, and pray in the long summer days–these are the two extremities where times are short and the deeds are easy.
And it’s not a loophole–-Allah (سبحانه وتعالى) designed the universe like this for this exact reason! It’s in the above hadith! So take advantage of it!