It's difficult to convey how big a deal Tesco's issues have been in the UK–it's had very extensive media coverage, a parliamentary inquiry looks likely, and there are investigations ongoing by the Serious Fraud Office and several regulatory bodies. This has created a distinct lack of goodwill in the general public.

Regardless of the accounting issues, they've had other issues too. There's the perception they're losing their customer base: they're ceding the low end of the market to certain supermarkets (Aldi, Lidl, Asda) and the higher end to others (Waitrose, Sainsbury's, M&S), leaving nothing in the middle. So that's a problem for them, and one they'd need effective management to handle.

All of this is potentially salvageable, but it is very uncertain, so I'm not surprised people might not want to invest.