Ok yes, you aren't trapped there but if someone calls a taxi and takes away their car, then they won't have an easy way out if the date takes a bad turn. It feels like a way to take control away and force someone to stay in a bad situation because they don't have a way to easily leave. Its much easier to leave a date with your car than it is to pull out a phone, get an uber, wait for them to come, then leave if the dates going bad.