Voting and elections is administered at the local and state level. Would you like the Feds to take over all elections, including local and state elections? After all, liberals from other states would love to directly influence elections in conservative states and jurisdictions.
Penalties for voter fraud can be handled at the state and local level.
There are numerous other offenses that are primarily local and state crimes, but is backed up by a federal civil rights or constitutional statute and prosecution to keep the states and localities honest.