Even though English spelling is so irregular, native speakers still share a common writing system with little regional difference. When you refer to the moving organ in your mouth, you may pronounce it differently, but all native speakers write T_O_N_G_U_E, in such obviously “wrong” spelling.
Why? Why didn’t different regions develop different writing systems, since they have different accents and word-choices?
They did in the really old days, even 2 people sat next to each other spelt things differently (think of young kids learning to write). But in the 17 century they invented dictionaries, but
It was not until Samuel Johnson’s A Dictionary of the English Language
(1755) that really took off and it became the standard dictionary for 150 years that our (Brits) spelling became standardised.
It is all well and good having regional spellings when the only people to read your work are other locals, but once travel became easier writing also had to travel.
My husband would spell my pronunciation of the word bath as Barugh, as he is northern and I am southern.
But that makes written communication completely unfeasible, so we had to standardise.
A wiki link on dictionaries
As mentioned in a comment printed books also had the same effect, a very popular printed item could change/standardise the spelling of words
Source – logic and hundreds of hours of watching documentaries on social history