There are any number of reasons for this: I suspect the main is budgetary; there is continued reliance on found, usually pop, songs; a lot of the work is formulaic; some - art-house - films often don't have any score at all, or I may not be going to the right movies. For instance, though I'm a fan of composer Max Richter, I haven't seen the last film to which he contributed a soundtrack, Sarah's Key, despite his faintly terrifying contribution to Waltz with Bashir (2008).
It can't be coincidence that one of the greatest of all directors, Alfred Hitchcock, worked with some of the greatest composers in the genre: Dimitri Tiomkin, Franz Waxman, Miklos Rosza, Bernard Herrmann... One soundtrack I would highlight in the last few years is that for Tom Ford's Christopher Isherwood adaptation A Single Man (2009), which not only includes vintage hits but also mixes work by two composers: Shigeru Umebayashi and Abel Korzeniowski (plus a touch of Herrmann).
Composer Michael Nyman, notable for his work on such Peter Greenaway films as Drowning by Numbers (1988; pictured) and The Draughtsman's Contract (1982), as well as Jane Campion's The Piano (1993), is especially scathing on the state of scoring in cinema, citing derivative work and general condescension. At the root of his argument seems to be a lack of respect for the art of a composer to which, I would add in what seems to have become an increasingly (visually) stylised medium, the role of a great soundtrack.
For the record, one of Nyman's favourite bits of his own work occurs, perhaps surprisingly, in Michael Winterbottom's determinedly contemporary London movie, Wonderland (1999). He told a Time Out screening earlier this year, of the scene in which Gina McKee takes the N171 home late at night, with all that entails: 'The bus sequence is the best combination of music and image I've ever been involved in.'
UPDATE The same day I posted this, the wonderful Letters of Note site featured a letter from Audrey Hepburn, thanking Henry Mancini for his score for Breakfast at Tiffany's. It includes this succinct appraisal of a good film soundtrack: 'A movie without music is a little bit like an aeroplane without fuel. However beautifully the job is done, we are still on the ground and in a world of reality. Your music has lifted us all up and sent us soaring.'