Whilst I agree with you that all
politicians lie, I would say that's only because the voters want politicians to lie.
If you had a choice between:
Candidate A who promised to either increase spending on say the NHS by increasing taxes or alternatively decreasing taxes by cutting spending on say the NHS or
Candidate B who promised to increase spending on the NHS by "cutting waste" or growing the economy etc but definitely not increasing taxes or alternatively cutting taxes but not cutting spending by cutting waste or growing the economy etc
Then Candidate B would always get elected to be a politician.
Candidates that don't lie always remain as Candidates.