The phrase "massive proliferation" refers to a rapid and extensive increase in something. It implies that the thing being referred to is spreading or growing quickly on a large scale. Full definition
Buratai, at a briefing in Abuja, said the army also discovered that there was a «massive proliferation of small arms and light weapons in Taraba State, some of which had been recovered from warring parties, criminals and unauthorised persons.» (punchng.com)
Another area where smartwatches could see massive proliferation is in the workplace where companies could resort to doling out smartwatches to their employees for communicating with them. (goodereader.com)
I think we are just starting to see the complexity, side effects, and unintended consequences created by the massive proliferation of convertible notes over the past few years. (feld.com)