I believe there are two main points that could explain the lack of service now;
In the old days, airlines were run by staff who had come up through the ranks to their deserved high positions, whether this be pilots or ground staff. Now the airlines are run by 'accountants' who wouldn't know a 747 from a coach.
Passengers now are expecting more and more 'service' whilst demanding even cheaper fares.
So these opposing views continue to do battle. The airline wants to give less for the money and the passengers want more for less.
Whilst I thoroughly enjoyed my 40 years with various airlines, I'm very happy that I'm not involved now apart from using them to get from a to b
As an airline employee the old days really were the good old days.