by design they don't, i shall expalin.
you need a solar cell to collect / convert sunlight
most lights are small, so limiting the size of the soalr cell
small solar cells do not produce much energy (voltage / current)
this energy has to be stored (small batteries) small batteries are usuallly 1.2 or 1.5 volts, so two in series only gives 2.4 or 3 volts
at this low voltage the only thing you can really light is an led,(dim at best)
super bright leds draw a lot of current and would soon flatten the batteries so making them a non option.
I can give you a url of a site that does supply bright solar lights, but guess what, they have big solar cells and cost an arm and a leg.
to be honest you would be better off with wired garden lights