I'd say say thank you to Jim personally, but sadly he passed away a while ago. He was a very innovative man, which is remarkable in a publisher. One of the other things Jim and his cohorts implemented was a fan screening service for inbound fiction, basically fans would get submissions and rate them prior to getting to the Baen staff and family for final approvals and edits, while Baen are not a huge publisher compared to others they're the only publishing house I've never had reason to dislike, they're approachable and most of their writers are actively engaging with fans the BFL is a perfect example, all the books there are there because the authors said ok to it supporting the concept.
He doesn't purely write alternate history. However he rarely if ever starts a series as a trilogy and ends as a trilogy... I seriously can't remember any of his trilogies that ended at book 3.
I have to admit though I've enjoyed his writing over the years and this sort of involvement with the fans gives me another reason to like him and add him to a shortlist of authors who've gone above and beyond with fans, another is Piers Anthony one of the recurring characters in the Xanth novels (Jenny the Elf) was modelled off a fan who a victim of a hit and run. It was good to hear about her progress in the author's letters in the novels, and about other fans and their input entering the novels.
On a related note sometimes publishers will help with engaging with fans Jim Baen (owner and founder of the Baen publishing house a major publisher of science fiction) before he passed away established a free online library which had selected works from Baen writers such as David Weber (with their approval and support) which provide in some cases an introduction to certain series (for myself Weber's Honourverse books), and with their books is usually included a CD which includes all the previous titles in the series and other novels or stories that might be of interest. Sadly Jim has been dead for about 4-5 years now, along with some of the more engaging writers I've had contact with over the years.