It's fun to have these split blocks, you can make mirrored tracks.
I did almost all the blocks in TMO, and most of TMS and half of TMN. I did the planks on the side of the road in desert, I did the turbo ramp in the center in snow, the turbos on one side in snow. I did the Y shaped sections of highways in islands, and I believe I did the splits of TMN. And over the years, I discovered that the feeling I have everytime I come close to any junction, that feeling of 'did I choose the right path?' wasn't very positive.
TMN was just tons of variations of the same road block, mostly because of it's e-sports aspect , so it was easy to get these junctions done.
In canyon, closer to the TM Sunrise spirit in that way, we have a greater need of decorations and landscape variations, we need to do trees, terraforming, different types of roads, tunnels, etc... so the double path blocks are quit low on the todo list, you can achieve that with OffRoad or JunctionsToArena.
I agree the bowl blocks (that would be named ArenaLoopStartGTCurve2 and ArenaLoopEndGTCurve2) would add some new feelings and sensations. We didn't make the ArenaLoop at first to avoid breaking the 'real place' feeling that makes contrast and emphasis the unbelievable action (giant jumps, etc...) in a race.
Jumping above a house is a lot more impressive than jumping over a big block of concrete. The Bowls blocks are a step further to that 'strange spatial base' feeling (plus it costs a ton of polygons

) that makes them fun, but not top priority. Hylis may have other reasons in mind I already forgotten.
You will always miss some blocks, and you know, I miss a lot of blocks as well.
I always have... since the first Trackmania.
We are always a bit sad to not having done that block or that feature, to not having polished that menu or that texture, or that feature. Or to have "lost" time making that block instead of that that one.
There are so many things to do in all areas, TrackBuilders, RecordHunters, e-sports admins, CarSkins Artist, movie makers, etc... everybody wants it better.
Well, we are not as many as a Microsoft's Team working on Windows versions. Luckily Maniaplanet is not as big, but it's not a solitaire either.
Don't stop expressing that you miss blockA or blockB.
Just try not asking why they're not made : 1-we forgot, 2-we didn't have time, 3-it may be a mistake.
Anyway, that will give us experience to improve the future blocks sets in future environments.