Look at a globe. You'll notice that the water around the tip of South America/South Africa is one of the few bands of the Earth completely unbroken by landmass.

That's a lot of fetch for wind, which transfers energy to the ocean's surface, which travels as waves, which build up because there's no land damping from west to east. Throw in the Antarctic Circumpolar current and weather systems interacting with the Benguela current an Agulhas current... That's a lot of energy getting put into a relatively tiny band of water.

The Cape of Good Hope was previously known as the Cape of Storms based on the aforementioned confluence of forces generally making sea states miserable. The Good Hope part was what putatively happened after you got through it, and the seas you'd have to worry about would generally be calmer.

Very rough water around the cape of good hope. Comparatively calm water through the Suez and Med.

Hoping I'm not misreading and this is what you're after - basically, less predictable weather that is more prone to suddenly changing when going that route and also naturally given the extended period of time involved. Longer it take to go around, the more time for potential sea conditions that large container ships may not be safe in.