That's good...it's not siezed.
The next logical assumption is: FUEL delivery has become compromised.
Vacuum hose from intake to petcock has failed, split, detached, clogged, etc. ....OR
Fuel hose from petcock to carburetor has failed, clogged, split, detached, etc. ....OR
Screen in the bottom of gas tank has clogged....OR
Float needle has become stuck, or damaged, or clogged with debris such as rust particles,....OR
Debris has infiltrated the bowl and has clogged the main jet and/or the pilot jet....OR
Spark plug has fouled from burning too rich,...OR
Very seldom, but possible : the gas cap on the tank has stopped venting properly and created vacuum
inside the gas tank preventing flow....OR....??
It's not very likely that the spark has failed, but it is possible. Confirm spark when checking for fouled plug.
Good luck sir...