What are those legal reasons? I'm new to radio stuff, scanner stuff I'm pretty set with but radios and the fcc part number I haven't really studied yet
Under the GMRS rules, any transmitter used must have FCC Part 95 certification. There is no exception to that rule.
Electronic Code of Federal Regulations (eCFR) published by the Government Publishing Office
www.ecfr.gov
With the exception of amateur radio, most radios used in the USA need to be type certified for the radio service in which they are used.
For Marine use, transmitters must have an FCC Part 80 certification
For Aircraft use, transmitters must have an FCC Part 87 certification
For Public Safety/Business/Industrial, transmitters must have an FCC Part 90 certificaiton
For Personal Radio Services (GMRS, FRS, MURS, LPRS, CB etc), transmitters must have the appropriate Part 95 certification (differs depending on the different services).
Basically what the certification says is that the transmitter/transceiver meets the requirements of the radio service and can be legally used.
Such as:
FRS must have a non-removable antenna, not exceed 500mw or 2 watts, depending on the channel
GMRS must meet power/stability/emission requirements
The outlier is Amateur Radio, which does not require a certification on the transmitter (ONLY when used inside the limits of the amateur radio bands). That goes back to the days where some amateurs built their own radios (and many still do).
Under the rules, using a Yaesu FT-60, which has no certification on the transmitter, it would be against FCC rules to transmit with that radio anywhere else than on the amateur radio frequencies. And while some will knowingly hack the radios to do otherwise, it is specifically forbidden and it puts your licenses at risk if you do transmit with it.
Same goes for some of the Cheap Chinese Radios. Many of them do not have proper type certifications for anything other than amateur radio bands. Many of them are easily modified, either physically or by programming, to work outside the amateur bands. FCC has cracked down on some of them.
It's a good idea to read the rules for the services in which you are licensed. It can get a little complex, but we are happy to help you understand it. It is your responsibility as the one holding the FCC license to make sure all the rules are followed (regardless of what someone on the internet says).