Games being played with greater frequency because season started late so less rest time.So why is it suddenly overworked in games compared to usual so more subs needed?
If more subs will prevent it, why do we rarely make many?
You could also say the lack of break between last season and this, although by the same degree us having significant injuries when we had an extended break wouldn't support that. But then how many of our injuries are 'new' and how many are ongoing issues from last season or unrelated ones like Hilssner's breathing problem.
At the moment due to the games not being played during lockdown last season even though there wasn't much of a break for the players overall as the continued training the lack of high intensity from games reduced the wear and tear from overexertion while the training kept the muscles supple and it could in some respects be considered like an end of season break.Then five subs to finish last season did the same to reduce over-exertion.
So at the end of the year that would be consistent with a 'normal' length season and you'd have to see the effect on injuries beyond that time, but if they bring in five subs it won't be consistent with previous years.
IMO those clubs most calling for it have the largest and most capable squads anyway and could much more afford to rotate the team in certain games without losing much quality to avoid injuring players if they chose. Fact they're not willing to and want more subs instead is having your cake and eating it. If you're not willing to play these squad players to protect your stars then don't employ them and let others teams enjoy a bit of cake as well.