Granted it is a petty subject, and certainly one would not like to unduly increase one's workload, However it is quite disconcerting for your greeting not to be reciprocated and similarly to be sent off to the next sector with no salutation.
Courtesies are part of our ingrained etiquette, whether in person or over RTF. Should trainee ATCO's be being told not to greet their 'clients' than more and more the human factor in aviation is being lost.
UK is not the only busy airspace in Europe, but this trend seems to be taking root only here.