Yeah this oversight is quite disappointing. The mode is fun but not being able to plant really messes with your effectiveness as an attacker.
When attacking you're incentivized to pick up a dropped lance because it's on a reset timer, but if you pick it up and can't plant it there's no way to drop it besides getting yourself killed.
Time is a key factor in this mode so you end up wasting time for your team either way — don't pick it up (since you can't plant) and wait for a teammate to hopefully pick up the lance before it resets, or pick it up to avoid a reset and then wait for an enemy or something to kill you while trying to keep it in a good position for your team.
I guess I need to take some explosive with me so I can "drop the lance" for my team if necessary. I prefer to play Falck though so the only option is a grenade, and smokes are pretty useful in this mode so I'd rather not give them up.
*sigh*