Is playing cards without betting Haram? If so please tell me why?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

No doubt that playing with cards (deck) becomes Haram if it leads to losing some right, obligation such as prayer or parents' obedience or losing any Divine duty. If playing cards does not lead to losing some right nor negligence of Allah's obedience, then it is a matter that spoils one's sense of honor, especially if one does it often.
The above-mentioned ruling is if playing cards is just for playing, i.e. not for compensation. But, it becomes strictly Haram if is played for compensation, since it becomes a form of gambling.
Allah Says (interpretation of meaning): {O you who believe! Intoxicants (all kinds of alcoholic drinks), gambling, AlAnsâb, and AlAzlâm (arrows for seeking luck or decision) are an abomination of Shaitân's (Satan) handiwork. So avoid (strictly all) that (abomination) in order that you may be successful.} [5: 90].
Also, it becomes Haram if it leads to hate and enmity. So, a believer has to observe time and to spend it in useful things Here and Hereafter, since time is life and life is the dearest of one's belongings and Divine blessing for which one will be held responsible.
A Prophetic Hadith reads: "Son of Adam will remain standing on the Day of Judgement till he is questioned about five things: his age, how he spent it; and about his youth (body) as to how he consumed it; and about his wealth from where he acquired it and in what activities he spent it, and about his knowledge and how he utilized it" [ al-Tirmizi ].
Another Hadith reads: "People are losers in respect of two bounties, i.e. health and affluence, as a result of which they do not worship Allah as much as they ought to do" [Reported by Imam al-Bukhari ].
Allah knows best.