When creating an event for motorcycles and use the deletable flag, they do not despawn after the lifetime. They do however despawn if the wheels are removed and placed back on the bike. Than they despawn. Other vehicles do despawn as intended when they are used with the same event parameters

<event name="Vehiclebikee">
        <nominal>1</nominal>
        <min>1</min>
        <max>1</max>
        <lifetime>300</lifetime>
        <restock>0</restock>
        <saferadius>1</saferadius>
        <distanceradius>1</distanceradius>
        <cleanupradius>1</cleanupradius>
        <flags deletable="1" init_random="0" remove_damaged="1"/>
        <position>fixed</position>
        <limit>child</limit>
        <active>1</active>
        <children>
            <child lootmax="0" lootmin="0" max="1" min="1" type="Motorbike_01_Blue"/>1
        </children>
    </event>
i have used this exact event setup on other vehicles like trucks, humvees, and cars. those do despawn once exited the vehicle

For motorcycles to despawn once the life time is up and a player is interacting with the vehicle.