Mustafa's business model works very well for the area it is in. As long as that area - Little India/Serangoon Rd - remains as is, then Mustafa will continue to thrive, particularly since it pays no rental but might collect rental from others.
Mustafa is in effect a one-trick pony where its business model cannot be replicated anywhere else nor is its owner seemingly interested in replicating it anywhere else. But it is a highly successful one-trick pony.
People who visit Mustafa inevitably go there for a purpose. In other words, 90% of the walk-in customers would likely walk out with a purchase. (I have made just 1 visit to Mustafa, 2 years back. I went over to get something specific, discovered it was stocked there but was shocked that it was quite expensive. Nonetheless, because I had made the visit, I bought it and walked out. I can't see a need for me to return.) You compare this to regular shopping malls, where perhaps only 20-30% of the pedestrian traffic goes in and buys something; most other people are at malls to window shop.