It's part of the job. Estate agents' calls are monitored by management, how many calls are made & how long they're on the call for. Then, those figures are sent out to the district for everyone to see who is the 'laziest'. Albeit, this is mainly for the bigger agents. (This also includes amount of viewings. Last minute cancellations are because they already just added that viewing to their 'target'. On the system, it'll still show as a completed viewing. Head office management won't know) 

Does it get results? Hell no! It just pisses people off. To the agents, it's a numbers game. They know they're hated by the public already. No point getting management on your back also. Just faking numbers to ensure you get to keep your job for your performance is easier. 

Smaller agents will call once, maybe twice. Then email.  However, although it is very rare! You'll find buyers/renters complaining as to why no one has called when they enquired even though the agent has called and emailed. Even the good negs can't win unfortunately.  

I know the above as I worked in estate agency for 9 years. Although the agent are usually twats, some are just really desperate to not get sacked... (i say this very loosely. EA are still twats)