There's no quick answer here. Epistemology (how we go about knowing things) is an involved topic.

Looking at the birds and the trees - and other life forms out the window - are cited as evidence for a god. "The evidence is all around you!".

But we're not ignoring anything... instead, virtually no evidence is actually provided. What is evidence? What counts as evidence? Many people seem to think "evidence" is merely anything that's consistent with what they're saying. There's some minimum requirements for something to qualify as evidence.

Evidence should be:

  • Repeatable/reproducible
    (This doesn't mean necessarily that the original phenomenon is reproducible, but the evidence itself)
  • Logical (logically follows, and doesn't employ any logical fallacies - hint: "We don't know how else this could have happened" doesn't qualify)
  • Exclusionary (should be concordant with a small set of possibilities, ideally just one). If the asserted evidence implicates contradictory claims, it has no value as evidence.
  • Objective, or not of a mind (no "I had a vision" claims)
  • Presentable (no "I have the evidence, but I can't show it to you")
  • Follows Occam's razor (accounting for the most data with the fewest assumptions)

Each requirement can be argued as to why it's vitally important.

Missing some of the above requirements plummets the usefulness of the "evidence" in question. With respect to the God assertion, we haven't been presented with anything that'd really qualify as evidence, let alone good evidence. Mostly what we get are waves of common logical fallacies without any attempts at empirical confirmation.

Keep in mind, arguments are not evidence. Arguments take evidence and try to make a case, but aren't evidence in themselves.

Even if we had one good piece of evidence, that's not enough. You still need to have sufficient good evidence to build a solid convincing case, especially if it contradicts established science and observation, or is heavily unprecedented.

Imagine you're at a car dealership, and you ask why you can't purchase a particular car. The salesperson says, "Because you didn't bring any money". A reasonable person wouldn't think that giving $1 to the salesperson, and saying "Yes I did! Here it is." means the Corvette is now purchased. No, it costs $25,000. You're $24,999 short. The salesperson just phrased the problem poorly.

Atheists make this same mistake frequently when asked "Why don't you believe in a god" and the atheist replies, "Because you haven't given any evidence."

Different claims have different levels of evidentiary requirements (The Corvette costs $25,000, but the Aircraft Carrier costs $1 Billion). You have to factor in how precedent the claim is. If you claim to own an ordinary dog, we may just take your word for it. If you claim to own an alien dog from another dimension, you have quite a bit more work ahead of you, to accumulate enough evidence to make your case.

God is unprecedented in terms of the observable world. For example, we have no examples of minds that can exist apart from a physical brain, let alone outside of space and time. It'd be one thing if there were gods walking up and down the street regularly, and you could talk to them. Since there aren't, the amount of evidence needed to make this case is astronomical. You'll need a lot of evidence, and it needs to actually be evidence, and not just arguing, "Yeah but where does morality come from? Hah! Since you have no answer, the answer is God by default!"

It'd be like asking us - "Why do you ignore Zeus? He's throwing lightning bolts all over the place and you're just ignoring him." In the modern day, we understand that lightning is just the electrostatic breakdown of the air between the charged clouds and neutral ground.

We don't believe any evidence has been presented to ignore.