Well,,you have a good point inhere,,and no (WISE) human ever would deny this and ignore this fact,,But Kindly allow me to explain for you why they do this,,and how God said that faith only is NOT ENOUGH at all .. as it mean nothing in the sight of God without proving this faith by worshiping God and follow his laws..not just to be a believer (Just in case ) !!! if God exist !! no,,this is still not enough ..
to answer your first point about why atheists ignore the truth about God and reject him,,Well,,Kindly be aware as i talk with atheists since (years) now,,and all types of them and from different locations and ages,,but the point is ,,the (Majority) of atheists ignore God not cause they are not sure if he exist or no..actually Most of them specially those who tried to check about the matter and the proofs ALREADY know that God exist maybe more than many of the simple believers,,(dont be surprised) this is 100% true,,as they always try to start and use science to disprove that God exist,,and then they see how science totally prove and confirm that universe has a Creator and when they study deeper they see with proofs how God exist for sure .. but the real reason why they ignore him as they cannot control themselves and their lusts and want to enjoy the life the way they want ,, for example they hate how God forbid any sexual relations outside the marriage and drugs and all this bad stuff,,!! so they chose to be atheists as they cannot obey God and i swear for you this is 110% true not just 100% only,,as i know and talked with ()THOUSANDS) of them so its not me imagine this about them or assume,,unforantntly this is the absolute truth about the case for most of them..and in same time to be fair to them and honest,many of them convert and chose to be a believers when they see lots of proofs..and when someone who is well informed about the matter help them to see the truth.
and your second point about being just a believer (Just in case if God exist !) also is not enough and not fair,,as to be a true believer you must do good deeds like worshiping God according to his terms by praying and fasting and doin charity and help others,,,etc...which is all of it a nice things and good deeds and make the world better for all of us and for everyone and in same time mean that this person truly obey God and want to be a true believer,,not just to have faith (just in case) and in same time do whatever you want..even Logically if a person Love God so this person will be indeed thankful for him for all his countless graces to all of us and also will Love to pray and worship God even by himself ,,!! or logically this person dont really love God ! just claim this by mouth !! which is not enough according to (ALL) the holy texts and what all the prophets said and taught..and in same time fair enough,, so kindly try to have better relation with God and trust me you will love this and understand why its very important matter..