Dead simples. Rule of thumb, if you pay more, there is more time available for chasing others on your behalf. If you pay more but other side doesn't, then your guy/gal will run around in circles waiting.
If you pay cheap price, you only paid for doing the paperwork, you did not buy any chasing up time. Paperwork written, put in post - ignore until it boomerrangs back. If it doesnt boomerang then nothing happens.
Decent estate agents employ chasers. They ask for contact details for everyone and from the go get they phone every f****r involved every few days until the deal is done and they get their fee. Anyone holds it up gets hassled until they pull their finger out.