The 2.4 Ghz spectrum was opened up for general use because it has relatively poor long distance characteristics thanks to it being absorbed strongly by water.
Interesting mention, and why microwave ovens use 2450MHz, water absorption helps keep RF signal local.
This lead to an explosion of use in the band where your average apartment building has dozens of devices competing for the spectrum.
Back in the days when ships were wood and men were steel, frequencies were allocated to business and public safety 2-way radios, broadcast radio, television, microwave backhaul, amateur radio, military, aviation, navigation, boaters, etc. But 2.4GHz was good for heating food as H2O molecule absorbs that freq. As these ovens are "noisy" FCC figured this will be good for general ISM devices. Then along comes computer/network/internet people wanting spectrum but it has all been taken (analogy of trying to homestead at the close of the 19th century). So only thing left was 2.4. They also seek out 5.8 and a few other slivers of spectrum. But don't think about opening up all spectrum. Cellphone and broadcasters are very possessive of their spectrum, and also many govt and businesses regularly use 2-way radios just like mechanics and plumbers use their tools. There was a time when radio had no regulation (1920s) with stations continually changing freq and increasing power, this lead to many listeners turning off radios and sales of receivers dropped (noted in Gordon West book on commercial licensing). Some services used to be licensed (CB), FCC threw in the towel but still asked manufacturers to keep their radio gear contained within that band.
Generally the FCC no longer enforces spectrum, they may call someone to locate source of interference on a cop frequency. I'm still amazed there are regular sales of 1.2GHz video transmitters that operate in the 900 to 1200 MHz band (aero nav band used by transponders) and all these RC drone sites selling 5.8GHz video transmitters (up to 2w) and everyone from commercial to hobbyists operate on this without any regard to licensing or station ID. But then it is the wild west so who cares? FCC will take action if a nipple is shown.
Over regulation is stifling innovation.
not really, the big megacorps are buying up spectrum then sell various devices where you need to subscribe and pay, pay user fees, fees for data usage, fees for using "excessive data", fees to upgrade, fees to fee.