alternative - A better word for "commoditization" when a type of shop becomes widespread

If Poundland and Poundworld are forcing other small, independent stores out of business, you could consider using market dominance which means:

Market dominance is a measure of the strength of a brand, product,
service, or firm, relative to competitive offerings. There is often a
geographic element to the competitive landscape. In defining market
dominance, you must see to what extent a product, brand, or firm
controls a product category in a given geographic area.

If the factor is more related with the brand power of Poundland and Poundworld, you could consider brand dominance which means:

The state that exists when the majority of consumers believe that one
brand outperforms all competitors.

Usage example:

Increasing market (brand) dominance of Poundland and Poundworld have resulted in closure of small and independent competitors such as Poundshop across the UK.

Brand dominance might not work better then market dominance as it is usually applied to a certain brand as is commoditization.

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