The most compelling reason was the constant clash between what I would want to do, what my constituents would want me to do, and what the party line happened to be.
To have to keep deciding between those three things must be hugely stressful. If for example I thought it was sensible to close a local hospital and transfer all its services to a new and better equipped hospital a couple of miles away, but my constituents wanted the local hospital to stay open, and the party line was something different again, what would I go with?
Then there's the mounting hostility towards politicians generally, for being out of touch with their constituents, pursuing expensive vanity projects and lining their own pockets. Female politicians especially are subject to a never-ending torrent of abuse, personal attacks and death threats. Many politicians have been forced to install elaborate security systems simply for their own safety.
And despite threadbare knowledge of the subjects I would be legislating on or making decisions about, I would have to add my shaky opinions to what might already be some totally misguided measures, with who knows what unforeseen consequences. What do I know about interest rates or planning applications or carbon emissions? No more than the average person-in-the-street.
No, I just couldn't have done it. I wouldn't have lasted six months.