Why some people are surprised I'm not sure.
Detroit was never going to match HR, for a few of reasons.
1- HR was a big deal at the time, QDs first major foray into this style of game. It also wasn't loved by all and sentiment has probably soured for some too.II personally loved it though.
2 - Beyond wasn't too popular, while some people like it many thought it wasn't as good as HR (still need to play it myself).
3 - there has been the controversy about QD that would have put some off.
4 - this doesn't include digital sales which would be important since HR didn't have digital at the time of release.
The only thing in its favour was the marketing budget but that doesn't guarantee sales.
The good thing for QD is that they spend less on games then most big companies so they won't need as much return as some potentially do.