Because something else always seems to come up that is too enticing to resist.
Writers' guides suggest creating a website or blog long before the 3-book contract is signed, before a publisher consents to publishing your novel, and even before an agent agrees to represent you. That's why I have been working on my blog's creation for months. The initial plan, before the revised Thanksgiving date, was to launch the blog . . . well, before now. Then those enticements started showing up, just as they do to disrupt my writing.
Weddings, reunions, and funerals all consume the discretionary hours of a person's normal life. Plans change as emergencies and other unexpected situations arise. Then the hours scheduled for writing the next chapter of that current novel disappear, turning scheduled writing hours into discretionary hours. The trick is to keep the writing hours in the non-discretionary column.
Which projects or daily chores do you have difficulty completing, what hours do you find almost impossible to keep in the non-discretionary column?
The obvious solution, easier said than accomplished, is multi-tasking.
The next time an unexpected event presents itself, I'll continue to write between doing laundry and packing; while waiting for the last boarding call to wherever; and during the flights as I eat my salted pretzels, rather than viewing The Karate Kid for the third time.