Shouldn't people be angry that this was not reported by our mainstream news so we can all make decisions based on complete information?
That depends. There are several important aspects of this case, notably the pitifully small fraction of his sentence that was served custodially. Is that typical in Maryland? If so, then that aspect of the case is only remarkable insofar as it's a part of a larger pattern of releasing criminals very early.
Notably the perp is also a Guatemalan subject to a final order of removal. Do those subject to final orders of removal commit heinous offences at a higher rate than average? If not, then that aspect of the case is not remarkable.
Seemingly his release from Maryland's custody was coordinated with ICE picking him up. Is that kind of cooperation unusual?
It's an interesting story that draws attention to Maryland's custodial practices, but artificially boosting stories to national attention without contextualizing their level of remarkability can be a form of bias i.e. if those subject to final orders of removal commit heinous offences at average rates and the custodial sentence served is typical then reporting on just those heinous offenders who happen to be subject to a final order of removal who are released very early provides not only incomplete information but creates an actively misleading impression.
So no, without more context I don't see why one would be angry that this wasn't made into national headlines. News is by its nature in the long run an aggregate of anecdotes, which does not make it data for making decisions from unless that aggregation is filtered to remove biases of editorial decisions. Which is damn difficult because the more different notable things you can cram into the same story the more likely it is to be reported on, which biases towards the unusual (that attracts eyeballs) rather than the typical (that you want to make decisions based on).