How many supermarkets does Hastings need?

Why does a smallish place like Hastings and St Leonard’s needs so many huge supermarkets?
    We go to Sainsburys in Sedlescombe Road – it was the first one we ever saw coming in on the A21.       That on its own is as big as anything we had in Birmingham, but later we discovered an enormous Morrisons, a colossal Asda, and what we understand to be one the biggest Tesco superstores in the UK.  Who goes to all these stores?  Do they do enough trade?  When we visited Tesco, the vast aisles were almost deserted.
   Also, all these stores cluster in the ‘middle’ supermarket band.  We understand Hastings has some very deprived areas, yet there seems to be only one branch of one discount supermarket – Lidl.  No Aldi.  At the top end, no Waitrose either. The little M and S food hall in the centre of town is always rammed, so clearly the top end of the market exists, as well as the discount end… I guess land must be cheaper here than in Birmingham, and the Council more willing to grant planning permission for these monsters. 
   Enough, I say, unless it is a Waitrose!  Our nearest are Eastbourne and Tenterden – all well over 20 miles away…..