Good trouble free tenants are hard to find. My last tenants (young professionals) were a nightmare and I couldn't wait for them to leave and because they left the place in a mess, it was hard to find new tenants. If a tenant was through a realtor in the UK and the tenant renews you have to pay a renewal fee so often most people don't want a tenant to remain as it can cost more, especially if the rent has not been raised to cover it. It doesn't matter how good their references are as I had a professor with his family staying and they were also a nightmare,( they broke the contract and left owing bills) so sometimes you are glad when a lease has expired.
Yes, I can imagine that, but that is why they need to pay a couple of months in advance, so that if the tenants leave damaged stuff they don't receive the deposit back, it seems more than fair.
Well if a tenant doesn't say that they are going to renew their lease, then the landlord shouldn't be surprised or hurt if the said family decides to pick up and leave. They have fulfilled their lease agreement and irritation should be part of the reason to leave.