'Star Trek Discovery' (or DISCO) has been a controversial move for the franchise. In America the program has been exclusively on CBS access, the very limited streaming service. The show has also departed from the previous series by having a singular main character and neglecting the ensemble cast styles of its older and more successful predecessors. This has led to the show getting bad ratings and even worse reviews online.
The Picard series is set to bring in a massive audience but will stream on Amazon prime outside of the US
Airing on E4 could be a new chance for the show to bring in a broader audience and keep DISCO going for future series. Currently, the fate of the show is tied to the highly anticipated Picard series. Fans are much more excited to see a return of Patrick Stewart and his co-stars than the next series of DISCO or any of its planned spin-offs. The Picard series is set to bring in a massive audience but will stream on Amazon prime outside of the US. It's unknown how this will affect the future of DISCO, but it's likely that it will also migrate over to Amazon as well, as the two series will inevitably tie in to one another.
This is probably why episodes are coming to E4, so that people who have chosen Amazon over Netflix are not lost when the two shows show up on Amazon Prime Video.
The future seems uncertain for Discovery. The show was never as successful as producers hoped, and being moved around from outlet to outlet could bring in a bigger audience, but will more likely alienate what little audience the show already has.