Oh yeah there are a lot of factors. Tamping is very important. If they can get into the interior of the structure rather than place on top or underneath it keeps most of the energy from traveling away from the structure. People also don’t understand that placement isn’t as easy as it looks. All of the explosives don’t automatically go off just because they are next to each other or even touching. “Military grade explosive” doesn’t mean stronger. It means they are very stable and hard to set off. Just in training I’ve seen half of a 20lbs charge of C4 blown off without detonating.
Many bridges in Germany built during the Cold War were designed with dedicated compartments in their structural parts to facilitate blowing them up. If a Soviet/East German Invasion had occurred (which was always considered a possibility during the Cold War), army units would, within hours, have dispersed to bridges in their area, filled the compartments with explosives and blown the bridge up to slow down the advance of the invaders.
Obviously each case is different, but damaging the structure can make it dangerous for tanks, which are very heavy. When the Germans failed to destroy the Ludendorff Bridge, a critical remaining bridge over the Rhine, but severely damaged it, the US Army was able to cross it with tanks. The US Army egineers tried to reinforce it, but it eventually collapsed after 10 days, although not before 25,000 troops, with accompanying tanks, artillery pieces, and trucks, were able to cross the Rhine, which shorted the war.
In the Battle of the Bulge, the Germans needed to move a large number of tanks and damaging the bridges enough to prevent those would have stopped the offense, even if infantry could cross them.