Often over time locks require maintenance to perform properly and being as they are mechanical devices, are just as prone to lack of maintenance as your car or any other precision piece of engineering. If your key is sticking in the lock here are a few pointers to look out for:
Next year Google is probably going to introduce advanced verification for certain trades in the UK to be able to show their business on Google. At present this is happening in the US for certain trades such as Locksmiths in particular.
It may sound implausible but many locksmith company owners, especially national chains and franchises, simply train their locksmiths to drill out old locks and then replace them with new before trying anything else. This is obviously to save time on the job, charge for new parts and get the maximum profit out of the customer. This is clearly not good if you are a customer who suffers from the experience of needing a locksmith repeatedly due to being prone to losing keys.