Why's Russia using 'suicidal' zombie wave tactics on Ukraine frontline?

Why's Russia using 'suicidal' zombie wave tactics on Ukraine frontline?
So-called 'zombie wave' tactics deployed on the frontline in Ukraine are, in effect, suicidal attacks that are allowing Russia to only make small advances and failing to hold territory, a security expert has suggested.

Ed Arnold, a European security expert at the Royal United Services Institute (RUSI) defence think tank, suggests the tactic of sending inexperienced fighters with little training in mass waves towards Ukrainian forces only results in a very slow, grinding attritional assault with no large-scale changes on the battlefield map.