Simply put, it's their age-old tradition. In fact, many Europeans ask why North American race circuits are all but universally “anti-clockwise”.
The origins of the various traditions are seemingly complex, and certainly debatable, but as I understand it late 1700s American horse racing power brokers purposefully created a US standard of left-turn-only racing, in defiance to England's centuries long right-hand standard. Then later America doubled-down and did the same exact thing with field and track. Olympic standards went back and forth in the early days of the modern Olympic era, but world pressure to standardize one way or the other happened to fall in a pro-American era, and basically the world adopted the American left-only standard for track and field – as I understand it - and this in turn influenced just about every other 'rotational sport', if you will.
Then later still, America adopted the German left-side automobile standard, and roadways, and this led to the natural adoption of left-hand race circuits here, and I believe that bit is actually well documented – why left-hand wheeled cars race turning mostly left.
All the while right handed race circuits never lost hold in Europe, from a time before automobiles.
Germans invented automobiles as we know them, and the French invented the Grand Prix format, so one would think they would have also went with left-handed race circuits (both F1 and MotoGP - and all their precursors), but apparently they stuck with the old-school right hand turn standard, which was helped considerably by the fact that certain infrastructure was already built.
(Note: A Brit will no doubt summarize this all quite different: ~“Brits invented the standards in motorsport that all of Europe now uses.” : )
But Romans used a sun dial. A post sticking up in the Northern hemisphere, as the sun moves across the sky East to West, the shadow moves “clockwise” around the dial.
(So basically I have no idea what I'm talking about, but your question hasn't been answered so I'm giving it a go with this "straw man" post.)
I'm going with “it's simply their age-old tradition”., and you fill in the blanks as to why that is.