They don't just contradict eachother : all but one contradict themselves in trivial matters, and do not see that as a problem. The last one is also not perfectly free from contradiction, but at least it makes an attempt to not be contradictory. That's because Christianity's bible is written by the same people that invented logic. It is generally believed that science developed under Christianity where it would not develop under other religions because Christianity saw nothing wrong : that logical contradictions cannot be is part of the religion after all.

Islam puts it quite directly in the quran : "None of our revelations do We abrogate or cause to be forgotten, but We substitute something better or similar--Knowest thou not that Allah hath power over all things?....Would you question your Apostle as Moses was questioned of old?"

(a lot of verses in the quran have this pseudo question-answer format)

This pretty directly says that

1) there are contradictions in the quran

2) in those cases the later verse is better

(it is known as the principle of "abrogation" and it has recently been used, for example, to scratch allah's three daughters out of the religion in what has become known as the satanic verses incident)

Note that 2) is an islamic legal principle that has been copied into pretty much every legal system on the planet. Earlier law systems, like the Roman one do what Canon law, or Jewish law do : they claim there are no contradictions, and they do work to eliminate them when they find them. America's legal system calls this principle : "lex posterior derogat legi priori".

Also, this is true in at least part of your life : modern law does not try to be contradiction-free. Neither does science. There's a complex history behind that, but it boils down to that the attempts to make science contradiction free were all thoroughly disappointing (e.g. http://en.wikipedia.org/wiki/Constructivism_(mathematics) ) . So now if 2 theories explain 2 different things very well, then we accept them as true even if they obviously contradict one another. And that's in exact sciences.

That is something I always wonder about "religion is contradictory so I don't believe" statements : they preclude belief in pretty much anything. Do you really don't believe math works because of the contradictions that ZFC ? Physics ? Did you ever even bother to check ? The main example I give that people tend to know about is that relativity flat-out says space is continuous, and it's silent on anything other than gravity, and an essential property of the standard model (which also states space is quantized, not continuous) is that there can be no gravity force (the graviton is a contradiction in that theory, so there can be no gravity fields).

Science is thoroughly utilitarian, and when it comes to a utilitarian view, obviously religion has it's worth (one might even say you'd prefer Christianity due to the accomplishments of it's followers).

So the fun part is that for the vast majority of people making statements like "religions contradict" is itself a contradiction in their thinking, they're simply not aware of it. I think this makes it pretty sad, actually.

People don't follow religion because it's (currently) easier. That's reality, and contradictions have nothing to do with it, aside from being an excuse.