There were reasons for the way the fighting was conducted too, and the popular idea of "trench warfare" being the norm on the Western Front for the whole 1914-1918 stretch is misleading. As with pretty much everything in life, things were a little more complicated than that.

The excellent /r/askhistorians forum has had some good coverage of this area in the past. Try this overview for a start:

https://www.reddit.com/r/AskHistorians/comments/37epxy/i_kep...

Or this seven-part epic answer regarding Verdun and the Somme more specifically:

https://www.reddit.com/r/AskHistorians/comments/32t8bn/world...

or more from the Western Front section of their FAQ:

https://www.reddit.com/r/AskHistorians/wiki/wwi#wiki_western...

Indeed, much of the criticism seems to be centered around the general theme of, "Charging machine guns over open ground didn't work the last 300 times we tried it, but maybe today will be the day."

With enough artillery and men it actually did work in many cases. The large scale assaults regularly made progress measured in miles. The problem was that you couldn't meaningfully continue an advance or exploit a breakthrough. Once you left your trenches you also left your supply lines. The enemy could respond to any breakthrough with overwhelming force mobilized by their own rails and roads.

It worked quite well in their grandparents day over the same ground (more or less) with the same opponents in the Franco Prussian war.

Unfortunately technology improved and trucks supply ammo to modern machine guns mean it doesn't work so well anymore.

Unfortunately, they were limited by the technology of the day - not the lack of mechanized forces, but the lack of portable radios. Charging across the no-man's land, while high in casualties, usually worked for getting an initial penetration of the other side's trench system, but without radio to coordinate reinforcements, artillery support, and a further exploitation of the breakthrough they would quickly fall to counterattacks. And then the bloodiest bit of the offensive, the initial breakthrough, would have to be repeated again.

Yeah i recall reading about how they would attempt to roll telegraph wire out as they advanced, only to have it snag on something or get cut by artillery blasts.

Yeah, even phone lines to established positions had to be buried to keep from getting cut by artillery bombardment.

I think it did relate to mobility and supply chains as well. But, yes, the bottom line is that costly long-planned breakthroughs invariably ended up getting bogged down.

Sometimes the objectives for a battle are a little more complicated than breaking through - holding actions, diversions, rearguards etc.

The British Expeditionary Force, and lots of the regular French Army, was sacrificed to blunt the initial German advance. British commanders were clear that the completely new army they were building would not be ready until 1916/7 but a mix of politics and necessity meant they had to be sent in earlier. Allegations that Britain would "fight to the last drop of Russian blood" - which had echoes of the Napoleonic wars - threatened to undermine the alliance.

The British attacks during Verdun were to relieve pressure on the French by diverting resources elsewhere. Every German machine gun, soldier and shell diverted away reduced French casualties. Given the horrific conditions and casualties there was a real risk of either a French mutiny or the Government deciding it could no longer pay the price. In the harsh logic of the time the losses at the Somme were a price that had to be paid to keep the allies in the war.