Home Depot/Lowes are good counterexamples of retail where profit margins are increasing, and some of it is surely due to them killing the competition and being in a high barrier to entry retail sector.
The logistics of selling the things Home Depot and Lowes sells is much harder to replicate than Target/Walmart/grocery retail, so the profit margins need to get bigger before a competitor will want to invest in the market due to the higher risks.
https://www.macrotrends.net/stocks/charts/HD/home-depot/prof...
https://www.macrotrends.net/stocks/charts/LOW/lowes/profit-m...
The logistics of selling the things Home Depot and Lowes sells is much harder to replicate than Target/Walmart/grocery retail, so the profit margins need to get bigger before a competitor will want to invest in the market due to the higher risks.