The popularity of a word may rise and fall over the years. A word whose use has been multiplying for some time is the adjective multiple, as shown by this Google Ngram of frequency in publications:
Until quite recently, the meaning of multiple tended to be restricted to the numerous aspects of a single thing. Common examples would be multiple copies (copies of a single thing) and multiple injuries (sustained in a single incident). This is why multiple can modify a singular noun, eg multiple choice, multiple personality, multiple authorship, multiple birth, multiple embryo transfer, multiple occupancy, multiple pile-up, multiple orgasm.
But in recent years multiple has been used more and more to mean simply ‘numerous’. In fact numerous has declined as multiple has multiplied:
The shift in usage is shown more specifically by comparing the phrases multiple injuries and multiple people. Obviously the word people is more common than the word injuries, but the modification of people with multiple is a recent phenomenon:
(The recent slight decline in multiple injuries may be due to the rise of the alternative term polytrauma.)
The use of multiple to mean simply ‘numerous’ is more common, I think, in the USA (and Australia):
But the British are certainly following along: