Looking at the graph, there has been £99 matched @ 2.02. There is also £40 more waiting to be backed at that price, plus another £50 @ 1.7, £2 @ 1.2 and £33 @ 1.18. So if you want to back you could back all of those prices for those stakes. These amounts are rounded, so might not be precise. Also, sums less than £2 don't show up on the price graph, so there might be £1.99 sitting at every other price. Click the little graph symbol to the left of the players' names to see what has previously been matched and what is available to back and lay at every price.
You're looking at the amounts and prices available to back, not what has already been matched. You've got things the wrong way around.
If you want to lay Vargas right now and have it matched immediately, you'd not be able to as the lay side is blank. That is there is no one wanting to back him to make the cut at the moment (except for possibly any £1.99 idiots). It doesn't matter what has been matched in the past, if you want a bet that is going to be matched instantly, there has to be money sitting there waiting to be matched.
You don't have to just take the prices on the screen like a traditional bookmaker though. You can make speculative backs and lays, like the person who has put up £40 to lay at 2.02. If there were no layers, Betfair wouldn't work as no one would be able to come along and just take a price, as the majority of people probably do. If you put up a lay at 50, it probably wouldn't last long and you'd get matched. If you put up a lay at 2.04 you may well get matched, although probably not straight away. Illiquid markets like this one, particularly in-running, are great as you can get people to take a silly price sometimes, although only usually for small stakes. Betfair has no palpable error so people can't change their minds later if they lay a price they didn't mean to or would rather not have.