Summary/claims: EA authors would gain readership and (I'd guess) not lose much money by working out impact-oriented ebook deals via their publishers with libraries. For example, publishers could arrange it such that any library that pays for five copies of a given ebook is thereafter given unlimited loan rights for free. This would take limited work and would increase the impact EA authors are having.

Reasoning: 

(1) People who are attempting to borrow a particular book from a library do not want to buy that particular book. So, an EA author (and whatever cause they're donating to) is less likely to profit monetarily from these potential readers. The positive impact "value" of these potential readers is contained in the actions they might take as a byproduct of reading the book. 

(2) However, people who have to wait weeks to months for an ebook are less likely to read it when it becomes available. That is, when an ebook is not available to read immediately to a library patron, the book neither brings the author financial gain or is as likely to influence people's actions.  

(3) Ebooks  require negligible resources to reproduce (e.g., it costs the publisher nothing, no trees are killed)

Data showing this is an issue at all: 

-I want to read What We Owe The Future for free. I'm #82 in line for the ebook and #60 for the audiobook at my library (estimated wait times 14 weeks and 18 weeks respectively -- there are at least several copies). This means there are 81 and 59 people ahead of me who are interested in reading these books and who, to me at least, now seem less likely to than they would be otherwise. 

-I'd like to reread a section of The Precipice. I'm #6 in line for it, and my estimated wait time is 12 weeks. 

-I've investigated other library-type sites online (Overdrive, Hoopla). However, the books are either not available or have similarly long waitlists. 

Indications There's Flexibility in Getting Ebooks to Libraries

-Plenty of libraries do "community reads" where a given ebook is has unlimited borrows. 

Conclusion

EA authors would gain readership and (I'd guess) not lose much money by working out impact-oriented ebook deals via their publishers with libraries. 

There are several ways to approach the expected value of this (e.g., might it make sense to give unlimited copies with any purchase so there is no wait list at any library?), but the situation could certainly be better than it is now.