Newer lenses need to somehow improve on their predecessors/competitors to make them marketable, and the trend has been on improving their optical performance (sharpness, aberrations, etc).
In the past, aberrations and lack of sharpness was embraced as "character" for lenses, or at least accepted tradeoffs for ultra-large aperture lenses. Heck, intentionally soft images were in vogue for a while. However, the current trend in the digital age has been toward edge-to-edge optical perfection wide open, with secondary consideration for things like bokeh quality, autofocus speed, handling. With that said, it has always been Leica-M's aesthetic to feature small lenses to go with their small cameras, and so they are willing to sacrifice some optical performance for that.
And finally, things likely have been helped by modern technology. I'm sure that having access to more computational power since the 70s has made it easier to create these more complex optical designs.
See if you can find photos of previous years' parade to get a sense of how the event will go and how other photographers approached the challenge.