Honestly, Jay just has better beat selection and more of an appetite for commercial/broad appeal.
Nas, by contrast, uses above average beat selection that's more hip hop oriented and has always limited the amount of commercial sounding songs he drops. Even comparing Illmatic to RD, RD has features of MJB and Foxy Brown while Illmatic is pure boom bap.
And even other Nas albums that have the occasional radio hit are mostly full of lyrical songs not made for the radio besides the single.
Nas, imho, is the better writer AND rapper. I always preferred Nas's mic presence and voice over Jay's. Jay has a nice voice too but sometimes it comes off too whiny and awkward to me at times. I can't explain it. And, lyrically, Nas is sicker than Jay when it comes to storytelling, rhyme schemes, metaphors, song topics, etc.
That said, I think Jay has slicker wordplay but some of that wordplay is forced af like Lil Wayne's. I remember brehs gassing up Jay's verse on "What's Free" on that Meek Mill album saying that Jay had the verse of the year and half of the bars on that track were forced af like the "Sign I failed" line that was supposed to be a play on Seinfeld or the jive turkey line. Not to mention that a good portion of the shyt didn't even rhyme and he started doing that weird Spoken word type flow. I've never been more disappointed at a so-called "top tier" Jay verse than that song.
I felt a very similar way about his "Neck & Wrist" verse which was also gassed up online but I wasn't impressed with the wordplay or even flow on that joint. Jay's flow was still on that off beat Spoken word wave while using some forced bars like the Faizon Love sub in the beginning.
But this is something I noticed with Jay and Nas in general. People hold Nas to a higher standard in terms of lyricism, flow, or even catalog. Jay, on the other hand, is much more marketable so, if he does the absolute bare minimum in terms of lyrics, flow, and subject matter, he'll get more props and praise for it because it came out of Jay Z's lips.
Overall, though, both are elite and top 10 DOA and that's all that matters. They have their strengths and weaknesses.