Although it's true that the system favours the legal profession and is, to an extent, a self perpetuating money printing exercise that could be done a lot more easily, they do all sorts of stuff and the money you pay does not all go to them (search fees, stamp duty etc). If you are buying, the tasks are different from when you are selling. If you are doing both at the same time, its the two added together. There are searches, checking title, co-inciding completion dates, preparing, agreeing, exchanging and examining documents and associated correspondence, including keeping you advised and arranging for you to sign things. They also act for the lender in most cases so have to convince them that all their security is dealt with. You have those costs to pay as well. The whole thing can get really complicated when long chains of sales and purchases are linked. Basically, they have to look after your interests and can be sued if they get it wrong.
Compare this with the estate agent who keeps a key (sometimes) and takes a photo. He charges a straight percentage cut regardless of how much work is involved and usually will not let on if he has a buyer lined up as this will mean they can collect tons of cash without having to write a single letter, print the particulars or even measure up. The rest of the time, they are buying flash ties and new cars. And they get between five and ten times what the solicitor charges. And, if you are buying, they are not even acting for you or in your best interests so you can't sue them so long as they don't actually lie (Cue tirade from the Toni and Guy, Armani and Porsche flash estate agent fraternity)