This is largely because early screen-space AO techniques weren't able to accurately estimate whether the pillar is freestanding (and shouldn't darken the wall) or if it is against the wall (and should darken the wall.)

Modern real-time ambient occlusion techniques can estimate the depth far more accurately and produce correspondingly more believable results, at the cost of performance.

https://www.researchgate.net/figure/Visual-comparison-of-dif...