In the earliest days one reason for this would have been that all the copies had to be written out by clerks by hand, using old fashioned pen & ink.
There was naturally a tendency to use abbreviation where possible –modern youngsters did not invent the technique with their texts & emails. Long words, frequently repeated, developed their own standard shorthand.
And so Association became Assoc
Say it quickly, over & over, & you get soccer.
So many of the usages which we deride as Americanisms in fact began in England.
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