As a retailer my reputation is extremely important, so when a customer of mine has a problem with goods I have supplied and fitted within a five year period, then I have to, and indeed want to, put things right. 

This is a rare occurrence but when it happens and the distributor/manufacturer will not supply free of charge replacements, then we bear the cost.

Why don't these suppliers give the same guarantee on the goods they supply us with as the guarantee we, by law, have to give under the Sale of Goods Act - five years?

Perhaps you might enquire of these distributors/manufacturers why this support is not given, as retailers might need to consider carefully where they source supplies from, if there is only a two-year guarantee on cabinet doors from the likes of their current supplier.