slimboyfat : I think the whole concept of “pioneer” is a bit of a throwback anyway. At one time pioneers were allowed to purchase the literature for a reduced price. This was the primary material benefit of being a pioneer, and in that context it made sense to ensure that publishers “qualified” to access this “provision”.
I believe the original reason for reporting field service was because colporteurs / pioneers were entitled to keep the income from the literature to defray expenses. In the article I Am Learning to Love the Colporteur Work More Each Day (Watchtower, May 15, 2012) it says :
By 1897, nearly one million Dawns had been distributed, largely by the colporteurs. Most of them lived on the small reimbursement they received for each Watch Tower subscription or book they placed.
In Zion's Watch Tower of April 1881 it first presents this idea of remuneration in the article "Wanted 1000 Preachers". It says (p.214) :
As few could afford to travel, pay their board and clothe themselves without some income, we propose to furnish the TRACTS and DAY DAWNS free, and to allow any such person to take subscriptions for the WATCH TOWER, using the money obtained from both of these sources, ("Day Dawn and Watch Tower," - the Tracts are free and must not be sold,) in defraying necessary expenses. Should your receipts be more than would be needed to pay expenses, (not at all probable,) you would be expected to make some returns to us.
It was only in 1943 that there was a time requirement and so a report was needed to show the number of hours spent in the ministry. In an article "Righteous Requirements" in The Watchtower July 1, 1943 it says (p.205):
[The Lord] says, 'Let us assign the field, the world, to special pioneers, regular pioneers and companies of Jehovah's witnesses in an orderly way,,,' He says the requirements for special pioneers shall be 175 hours and 50 back-calls per month ,,,; and for regular pioneers 150 hours and as many back-calls and studies as can be properly developed during that time. And for company publishers he says, 'Let us make a quota of 60 hours and 12 back-calls and at least one study a week for each publisher.'
Thereafter the number of hours spent became a measure of spirituality and a requirement for all of Jehovah's witnesses and not just pioneers.