Why is bartering uncommon in modern countries?
The main likely reasons why barter is not more common are:


The inconvenience of having to find another party who both offers what you want and wants what you offer.  
Even if such a party can be found, the possible complexity of negotiating a "fair" transaction (eg I'll do your electrical job if you'll clean my windows monthly for the next 3 months).
I don't want to encourage it, but for those seeking to evade tax, the comparative ease in many circumstances of doing so via a normal monetary transaction, but with payment in cash.


A further point is that most countries with VAT have a significant "VAT threshold", that is, a minimum value of annual sales at which businesses are required to register for VAT and charge VAT (where applicable) on their sales.  In the UK, for example, the threshold is currently £85,000. So an individual could provide services not exceeding that amount in any year and would not have to charge VAT.  If two such individuals were to enter into a barter arrangement, there would be no VAT saving. The Netherlands is atypical in that its VAT threshold is unusually low: 1,345 Euros (see here, table on p 2).