Since Triple H took control of 205 Live from Vince McMahon in January after the release of Enzo Amore, the Cruiserweight division has very rarely appeared on Raw (and I think not at all since WrestleMania). This was a deliberate decision, according to PWInsider.
One of the main reasons, PWInsider says, was to help keep the Cruiserweight wrestlers from being “overexposed” on Raw with what were essentially meaningless matches that most of the crowd did not care about. The thought is probably that keeping them only on 205 Live will help keep the division distinct rather than putting them in a bad spot on Raw and having them come off as not very important.
In February when Triple H’s takeover of the division was announced, it was reported that his idea was to bring the show back to what made the original Cruiserweight Classic special, changing up the roster a bit and focusing more on in-ring work.