Looks like Landon Donovan's move to RSL - and even his continuing to play at all - is being restricted by the league's ridiculous salary rules as implemented in the CBA.
Donovan's salary rate was right at the max contract value for a non-DP in 2016, but he and RSL are working on him being paid as a full DP in 2017. Two problems with that - first, a player that made more than 12.5% of his team's salary budget cannot sign as a free agent with another team if he would be a DP. Second, players signing as free agents cannot get more than a 15% raise.
As you might imagine, all of this is highly opaque and involves speculation as to why a deal hasn't been struck. There are waivers that could apply here, and presumably, RSL could just send a little GAM to LA for Donovan's rights, but there are apparently real problems in getting this deal done, despite RSL and Donovan apparently being in favor.
http://www.rslsoapbox.com/2017/1/7/14200176/rsl-interest-donovan-cba-mls-rules
http://www.rslsoapbox.com/2017/1/11/14241946/report-landon-donovan-deal-shaky-ground