alt Hacker NewsIIRC, this was because there was significant uncertainty about whether the network exec's would cancel the show after season 4, so JMS reworked things so that 4 wouldn't end on an open-ended cliffhanger if that were to have happened.
In the end, season 5 was given the go-ahead, and so now season 4 seems rushed needlessly.
The uncertainty is actually an interesting behind-the-scenes story that the mini-TV Channel hoping to grow up into a full TV Channel that B5 was distributed under was PTEN [0] and leading up to and during Season 4 of Babylon 5 PTEN split in a weird divorce to form the WB TV Network and the UPN Network. (It got its wish, it grew up into not one but two competing TV networks.) Season 5 was a last minute pick up/rescue by one of WB's cable networks, TNT. (TNT wanted more than just one season which led to the mess that was Crusade. As a Crusade fan, TNT was both the best and the worst of what could happen to B5.)
(History repeating itself, and Babylon 5 being cursed to ironic timing, the WB Network and UPN eventually remerged to become The CW. A Babylon 5 reboot project development was started at The CW this decade, just before WB Discovery decided to get out of the broadcast TV business and start a fresh divorce at The CW somewhat resembling the PTEN divorce.)
[0] https://en.wikipedia.org/wiki/Prime_Time_Entertainment_Netwo...