I have Bank of America and they also the monthly maintenance fee but you can get the campus edge account if you are a student. it's free for 5 years.
Are you sure the fee is new? They've had fees on various accounts for a long time - if you google it, you can see people complaining for years. Here's the list: https://www.wellsfargo.com/checking/ It appears you're on the Advantage package based on the $15 fee. Is it possible that you just naturally had one of the things that caused the fee to be waived until this month? I ran into that with BoA a few years back not realizing that I had dipped below some average daily balances that caused fees to accrue.
Credit Unions are owned by their members, there are not as profit driven as the big banks who are publicly traded and have shareholders to appease. Fees are lower or nonexistent. Yes you can still do online billpay, banking, even online deposits.
They look at it as a convenience for YOU, one that you likely would pay for rather than go through the hassle doing your own paper work and mailing/stamps.... The same thing happens with vehicle registration; send it via mail and it costs you more than to go to the office.
Their services are not free to you, they use your money to make money of their own. I think lack of fees can be contributed to simple competition between banks, but look at what's going on now-more banks are merging.