Well... that may have some causes:
1. A fluent Spanish speaker can understand any text written in Spanish that does not have any accent where it should be, so it becomes unnecessary in the "written slang", A.K.A. Spanish spoken/written in a bad way.
2. Accent, ñ, and "diéresis" (I do not know its name in English, but it is used in a few words like "pingüino" or "agüero") are not as common in Spanish as people think. You can perfectly write a long paragraph avoiding acute accents by using synonyms, and anyone will perfectly understand that paragraph.