Merhaba, I think we are using these words with "ler" suffix because of their pronunciations. If you use google translate and listen to their pronunciations you can understand what I mean. These word have "a" sound but we pronounce them a little thin.

-lar -ler are suffixes makes the noun plural. çocuklar, eller, evler, ayaklar, I have just recognize this as well saat -ler harf -ler kalın sesli ince sesli kalın sesli ince sesli yes normally it sounds kalın kalın( a,ı,o,u) or ince ince(e,i,ö,ü) there is an exception always

yes its just an exception to the rule. there are many words like these.