The reason for that was always because the seasons overlapped so there was no alternative (similar to Russian/Scandinavian teams in UEFA). Now with MLS ending in December and CCL proper starting in Feb/March, it would make very little sense to keep doing that.
I suppose the only motivation would be to avoid a confusing qualification process. The previous format was a bit ambitious
Not much of a league anymore though, they might as well call it the Concacaf Champions Cup again. We will see if this will be the format that finally catches on for them.