what was their reason to destroy it?
If the Germans were to hold it, the bulk of the Canadians would be unable to continue their advance.
Razing of Friesoythe
This made Friesoythe, west of Oldenburg, on the River Soeste, a potential bottleneck. If the Germans were to hold it, the bulk of the Canadians would be unable to continue their advance. 
what is razing of friesoythe? It was the destruction of the town of Friesoythe in Lower Saxony. in which country was that town located? Germany who was destroying it? The 4th Canadian (Armoured) Division
wiki:3154003
Razing of Friesoythe [SEP] Battle for Friesoythe
The Canadian advance continued across the Westphalian Lowland, reaching the outskirts of Friesoythe, a strategic crossroads, on 13 April. As it was early spring, the ground was sodden and heavy vehicles could not operate off the main roads. This made Friesoythe, west of Oldenburg, on the River Soeste, a potential bottleneck. If the Germans were to hold it, the bulk of the Canadians would be unable to continue their advance. Most of the population of 4,000 had evacuated to the countryside on 11–12 April. Several hundred paratroopers from Battalion Raabe of the German 7th Parachute Division and anti-tank guns defended the town.