The 146 is good at what its designed for, i.e. taking up to 40 tonnes out of 1300m runways. Unfortunately for it, this is not exactly a requirement of most operators. You ask it to do anything else that a 737/320 could do and its sunk.
Why? approx 2.1 tonnes per hour fuel burn mainly, taking into consideration only 90 pax and only travelling about 400NM in that hour. On sectors up to about 500 miles the slowness is not really noticeable but above that it gets fairly obvious.
Plus, as the thing can not always get above the weather, it can be fairly uncomfortable for pax. Often the 146 is bouncing around in the tops at 280, unable to get higher (non-RVSM approved), while the competition cruises along in smoothness a few thousand feet above.
Plus the freight capacity is rubbish and the cabin is narrow so to make it anyway economical with 6 across its not comfortable.
On the positive side: the leases are now dirt cheap, hence their continued existence in service. And they can get into LCY. And thats it really.
Well ok, they aren't as unreliable any more, though thats due to better knowledge rather than any innate good design.
The introduction of RVSM from FL200 and the new transponder requirements will probably kill them off altogether as the mods are apparently not worth it.