Travel insurance premiums

I  have been comparing travel insurance for two people under 60 for four days in europe. I have checked the excess details and there is no considerable difference between the different insurers. The policies I viewed are almost identicle and where I have seen differences, they are negligible.So why have I seen policies with travel insurance premiums as high as £30 and some low as £6-£7 (and the insurance is covered by big insurers for the low ones I found too). I looked at the small print and again from what I could make of it, there was no considerable difference.