The rotated axes balance the chart and make the achievements of Connors, Federer and Lendl more “central” to the story. (SRF are a Swiss news organisation…)
The composition feels unbalanced, and at a glance feels like there is less of a story in the chart. (Glanceability… that takes me back…. I first heard the phrase from James Cridland – Learnin’ from Virgin – then, as I noted in Powerpoint Presentations That Support Glanceability, Lorcan Dempsey dug into it a little bit more: Glanceability.)
It also reminds me of “banking to 45 degrees”, “the idea that the average line slope in a line chart should be 45º. This has been dubbed banking to 45º and has turned into one of the bits of common wisdom in visualization as determining the ideal aspect ratio [although it more specifically relates to] the comparison between the slopes of two lines, and the slope is the average between those two lines. So if the goal is to be able to compare the rates of change between lines, the 45º average slope makes sense as a rule” Robert Kosara blog post on Aspect Ratio and Banking to 45 Degrees.
The original statement comes from Cleveland, W.S., McGill, M.E. and McGill, R., (1988) The shape parameter of a two-variable graph, Journal of the American Statistical Association, 83(402), pp.289-300 [JSTOR], and I think I should probably read it again…
By the by, SRF are one the best news orgs I know for sharing their working – the recipes for the above story can be found on their Gihub repo at srfdata/2018-01-roger-federer – so I could probably have recreated the unrotated chart directly from that source, if I’d had the time to play.
PS see also: Five ways to read a scatterplot on the Datawrapper blog.