From a restraint owner, "“The rent I paid on 10,000 square feet [at the Park Plaza] was the rent I was going to pay on 3,500 square feet” on Newbury, he recalled."
When landlords get their rents to a certain pricepoint, they are loath to cut them. If they cut the rent for new tenant x, then existing tenant y will want his rent cut too,
And as for restaurants, the French Laundry recently spent $10+ million for a new kitchen, for a restaurant seating 60. (The chef owns the building, so rents aren't a problem) Readily conceded, that cost is an outlier, but still rents become a big factor when one has a big up-front cost in equipment and decor.
This site said that Newbury St had an average rent of $225 per square foot in 2015.
https://www.buxtonco.com/blog/top-10-most-sought-after-u.s.-retail-streets
How many meals at what price would a chef need to serve to afford those rents?