Bottom line with a PCP is that it's there to get you into a car that is more expensive than would otherwise be affordable or acceptable if you took straight HP or a bank loan. That is why it exists.
A £30,000 car with a £5k deposit on HP over 3 years would be £700 a month before interest and worth say £15k at the end.
A £30,000 car with a £5k deposit on PCP over 3 years with a £15k balloon would be £280 a month before interest.
That is why people PCP - the fact that once you've added the interest the actual cost over that 3 years is higher with a PCP doesn't really factor into most peoples decisions, either because they do not care or because the monthly payment for the cheaper overall option is not affordable anyway or is more than they want to spend on an ongoing basis, despite the fact it might work out cheaper in the long run.
It is now the most popular method of financing a car by some margin - the majority of cars are now purchased this way.