The core ideas for mobile phone networks (cells of radio towers, switching networks, etc), were explored in the 40s through the 60s and the first mobile phone prototype that kind of matches what we think of was created in the early 70s.

Mobile phones didn't gain popularity until the mid 90s, twenty years after the prototype and about 50 (!) years after the first rough tests. Mobile phones didn't gain widespread use until the 2000s even.

To say they only took 7 years to be adopted is ridiculous and ignores a ton of work that went it to developing them and making them useful.