Nothing technical.
It is not the visa that gets extended, it is the permission to stay.
A visa simply offers the right to enter a country, it is then down to immigration officials to determine whether to grant entry - and for how long. Once a visa has been stamped "used", that is exactly what it means; it is finished, it's purpose has been served; each visa has a 'use before' date which also time limits it's validity.
Those people residing in Thailand on extensions invariably do so off the back of an existing visa - the permission to stay under the terms of the visa gets converted to a permission to stay by virtue of extension (by reason of marriage/retirement etc). The mechanism for that is completion of a TM7 'Application for extension of temporary stay in the Kingdom' - upon approval the permission to stay is extended (usually) for 12 months. It is this permission that we 'renew' each year by completing a new TM7.
If Yorky (or anyone else) had a visa they could move freely in and out of the country; he hasn't, he can't. If he wants to leave the country he has to obtain a re-entry permit to keep his permission to stay live.
Alan the Builder can move freely in and out of the country because he has a visa. That visa is valid for 12 months and upon expiry it cannot be renewed, a new visa has to obtained (from Savannakhet, the only consul in the region that issues multiple entry Non-Immigrant 'O' visas).