Sprint is apparently the most popular race for spectatators and TV-viewers hence it gets the best day.
Self-fulfilling prophecy in recent years thanks to crappy courses in the distance races. Too many mens' races had devolved to pack races until the last 1-2km meaning no action until the last couple of minutes, and too many women's races had devolved to Johaug running - almost literally - away from the field, meaning no action after the first couple of minutes. As Eddy says, we need more variety in the courses to create more variety in the results and outcomes and how the races play out. Sprints will by and large always play out in similar fashion, because of the limitations of what can be offered on the short course, but distance races can offer a much wider range of outcomes... it's just that in recent years they don't.
The sprints are often a lottery, and can descend on a poor course into a crash-filled, luck-of-the-draw joke and make a bit of a farce of the spectacle (and of the concept of the sport as an endurance sport at heart)... but the format does guarantee that something will happen every few minutes as well as being popular with TV executives because it gives convenient spots to put the ad breaks without missing meaningful action.
The Team Sprint doesn't actually offer that, and is an appalling joke of a format with a lot of the weaknesses of the sprint and few of the strengths, but it does benefit over the conventional relays by having a wider field of potentially competitive teams, and the lottery nature of sprint courses also means that you can get some surprises more often than in the more 'pure' disciplines.
I had hoped that the hilariously awful spectacle of the entire field doing trackstands at the top of the climb in the Oberstdorf Worlds might have at least slowed some of the emphasis on the Team Sprint, but sadly I was wrong.