Even when systems have been well designed, architectural concerns often must yield to more pragmatic ones as a deadline starts to loom. Architecture is often seen as a luxury or a frill, or the indulgent pursuit of lily-gilding compulsives who have no concern for the bottom line. Architecture is often treated with neglect, and even disdain. While such attitudes are unfortunate, they are not hard to understand.
Architecture is a long-term concern.
Indeed, an immature architecture can be an advantage in a growing system because data and functionality can migrate to their natural places in the system unencumbered by artificial architectural constraints. Premature architecture can be more dangerous than none at all, as unproved architectural hypotheses turn into straightjackets that discourage evolution and experimentation. Architecture is expensive, especially when a new domain is being explored. Getting the system right seems like a pointless luxury once the system is limping well enough to ship. An investment in architecture usually does not pay off immediately.