Paul Heyman is an outspoken advocate who often blends the two worlds of real life and pro wrestling kayfabe together in a seamless fashion. Brock Lesnar's status as WWE Universal Champion hasn't changed the fact he's in a very interesting situation with WWE.
Heyman often comes down on the lack of competition WWE has to offer his client because Roman Reigns seems to be the only guy WWE is putting in front of Lesnar and the Universal Champion has defeated him every time so far. The multi-man #1 contender's match at Extreme Rules was canceled to complicate the matter even more and now Roman Reigns looks to be battling Bobby Lashley instead.
During Raw this week, Glenn Rubenstein of the Wrestling Inc. Podcast tweeted out "if Paul Heyman is actually watching RAW on live TV, why isn't he live-tweeting snarky comments about the commercials, like the rest of us?" After all, some timelines were filled with tweets about the commercials instead of the action on Raw.
Paul Heyman saw this question and responded in a way only he could by saying Raw is built around challengers instead of a champion like Brock Lesnar, therefore commercials are actually the best part of the show. It would be nice to see the Universal Champion every now and then and with Lesnar's next appearance still unannounced at this point, at least unsatisfied fans will have the commercials to watch.
Blunt answer to your interratory: Because when #RAW is built around CHALLENGERS (aka "wannabes") instead of a once-ever athlete (@BrockLesnar) and his humble @Advocate, the commercials are actually the best part of the show!— Paul Heyman (@HeymanHustle) June 26, 2018