do you park in areas exposed to sunlight? if yes, malamang that's reason why.

Wiper blades do get fried by the windshield. Once rubber loses its elasticity, obviously, hindi na maganda ang hagod sa glass

If you want, you can invest in those cheap "wiper-ups". I had those in my previous car and im satisfied with their performance (but not the looks hehe).

I dont need them anymore coz i always park in a shaded place.

Theory number 2 is madumi na ang winshield mo. Better buy some "Strip It" and start rubbing away at your windshield. (Or pagawa mo kay theveed)