Self-explanatory: there is no point to have an international break in Euro/World Cup years as there is no qualifying yet to complete, and it disrupts the league seasons for no reason. Clubs play Euro warmups before the tournament and those should be enough.
CONCACAF, AFC, and CONMEBOL are the three confederations with World Cup qualifiers this month. How would you propose each of them formats their qualifiers if they couldn't play this month? You have to think about more than just national teams in UEFA.
I realized that after posting but the clubs would just have to do without those players (as like when the African Cup of Nations happens).
All World Cup Qualifiers should be treated equally be FIFA. The African Cup of Nations has 16 countries. This month 61 countries will play World Cup Qualifiers. Let's say Bolivia played Argentina. I haven't checked the upcoming schedule, so I don't know who plays whp. Bolivia would have a much better chance at winning if no players on UEFA clubs could play because Argentina would be missing Messi and Aguero. I don't know any Bolivians on UEFA clubs off the top of my head, and I'm confident no Bolivians could score anywhere near as much in a top league as Messi and Aguero can.
Nothing wrong with the March international break. Club football can do with the break between January-May. There are three week-long breaks between August-December.