The Rams needed to make room under the cap when they traded for Fowler. They couldn't cut anyone who was on the roster at the beginning of the season because at that point their salary becomes guaranteed. Only guys signed to the roster after the first game and who were also making at least $2M for the 2018 season could have been cut to make the necessary room.
Here is the list of guys who fit that criteria:
1.) Jamon Brown.
Fowler's 2018 salary was $3,638,21 . The Rams' share of that was $1,926,113. [overthecap.com]
"By releasing Brown, the Rams save $1.7 million this season, while taking on just $188,704 in dead money. The financial ramifications are likely the reason Brown was given his walking papers, freeing up space to fit Fowler under the cap." [theramswire.usatoday.com]
"The Rams elected to waive Brown on Tuesday to make room for Dante Fowler ..." [nfltraderumors.co]
"Brown’s release is relatively surprising because many fans thought he could fetch a late-round draft pick in a trade with the dire need of offensive lineman around the league. That seemingly was not the case as the Rams needed to create a roster spot for EDGE Dante Fowler Jr ..." [nfltraderumors.co]
"As a corresponding roster move after acquiring edge rusher Dante Fowler, the Rams have waived offensive lineman Jamon Brown." [www.therams.com]
AlbaNY_Ram