It's a good question. It's pretty arbitrary, to be honest - with all of these things, despite the reasons I set out below - it's about what you want to highlight, and for what you want to use the data.

But there are two specific main arguments for presenting the data this way:

All prices in most countries that has VAT or GST or equivalent tends to be given tax inclusive. E.g. in most of Europe, a consumer can legally demand to pay the stated price if a price is advertised directed at consumers even if it is not specified that the price was meant to be VAT exclusive, or in some countries even if it is explicitly stated that the price is VAT exclusive.

So the first answer: Because when we otherwise compare price levels we compare the sticker price. If we otherwise treat the VAT separate from the goods, then that makes no sense. It's part of the complexity of trying to compare cost-of-living.

The other reason is that while the tax wedge on income is relatively stable across large parts of the population, VAT varies massively from person to person on the same income. A tax wedge excluding VAT tells us a lot about what proportion large swathes of the population will be taxed, and can't avoid paying.

But for VAT, a large proportion of it comes down to personal consumption choices.

To illustrate, let's assume 30% income tax (and lets forget about payroll taxes). This person has 70% left. Now, if I were to pay 10 percentage points of the gross to rent somewhere small, I have 60% left to spend. If I'm not bothered about a pension (stupid, yes), most of that might get towards VAT'able consumption (though some will e.g. be VAT-exempt goods like basic food stuffs). At a 25% VAT rate, that means 15% of my gross salary goes to VAT. If, on the other hand I earn exactly the same, but live in an expensive place that takes 30% of my gross salary, and I pay 10% of my gross towards pensions, I now have only 30% left to spend, and if make the same assumptions about what I buy I'd end up paying 7.5% of my gross in VAT, all through my own choices.

In reality, in the latter case you'd pay even less, as a larger proportion of the remaining cash would go towards exempt/zero-rated products like food (your total tax wedge would also be far lower, as in most countries those pension contributions would result in reduced tax).

1%-5% of the gross towards VAT is relatively typical even in countries with 25% VAT headline VAT rates. For someone with a low salary in a low VAT country it may very well end up being well below 1% (because low salary tends to mean a larger proportion goes to housing and food, leaving less for consumption affected by VAT)

So the second answer is that the VAT part is to a large extend under individual control, and so varies within the same income tax bracket, and so confuses the issue or a lot of the things you'd use the total tax wedge to get an indication of.

That doesn't mean that totals including VAT/GST or equivalent would be wrong/bad/misleading any more than excluding them is. They just show different things, and you need to be aware of different things when trying to use them in comparisons.

A lot of reports on taxation will include a variety of different breakdowns like this to give a fuller picture.