This is a loan-translation, or 'calque'. English is full of them. In different root languages retro=hind and sight=spect (v. roughly). Regard them as equivalents at your peril! People don't have '20:20 retrospect', for example or '20:20 sight'; they do have '2020 hindsight' and '20:20 vision'.
However, in the adv. phrase 'in *', they have very similar meanings. In loan-translations, shorter/spikier/home-grown constituents generally tend to go with a more concrete meaning. For example 'That project was a bit of a mess. In hindsight [perhaps 'with' or 'given' would be better than in'] I should've done things differently.' But 'In retrospect, my life has been quite interesting' - when you say 'in hindsight' you've got your sleeves rolled up, and when you say 'in retrospect' you're sitting in an armchair.