This thread from a month ago in r/Boston talks a bit about some of the challenges.

r/Boston thread

I think a lot of the challenge is that there's not enough people with disposable income that find Downtown Lowell a competitively convenient place to get to or live in. The walking infrastructure is terrible in many places with missing crosswalks, unreliable lighting, broken / missing sidewalks, large roads + highways with fast vehicle traffic (including lots of commercial trucks), insufficient market rate housing, and limited canal crossings which limit the pedestrian catchment area / market.

Lowell is also not ever going to be a competitive place for people to drive any distance to for simple things because the road network is poorly connected for actually visiting the city, in terrible physical condition, and poorly marked (they can't even manage to reliably paint lane lines). There are much easier places to drive and park, like Nashua. I can't imagine many people drive in to Downtown Lowell for casual discretionary errands / activities more than twice a week from anywhere really beyond the Lowell city limits.

I think comparing median per capita income - median rents also might help explain why Downtown and Lowell in general's commercial footprint is heavily focused on non-discretionary services like healthcare, social services, military recruitment, rehab clinics, and money transfer / cell phone shops. https://www.census.gov/quickfacts/fact/table/somervillecitymassachusetts,mobilecityalabama,lowellcitymassachusetts/PST045222

I don't think Lowell's business environment will change significantly without a massive influx of market rate housing inventory + some infrastructure improvements, or (regrettably) a wholesale gentrification of Downtown + the Acre.

I don't see any real political commitment or money going into market rate housing at scale in walking distance of Downtown Lowell.