Having served as an elder before resigning I can understand why 'Christendom's' ministers are full time.
You have to find the balance between, family, work, preparing for meetings (including non public meetings), rest, self study, field service, and I'm sure I left some items out. This is extremely difficult if you truly want to do a good job.
After thinking about it I came up with the idea that the 'perfect' elder would be a widowed, retired and strong financially, children grown up and taking care of themselves, and dedicated.
I tried to do my best, but it is impossible. Even if you give people a lot of your time (and neglect your family during the process) they may still be unhappy with your service.
A lot of people react quite unfriendly to elders. At the same time the elders are measured not according to what they do in the cong. but according to the time they report. And if you do not meet the average level of hours you are out.
And then there are the widows and orphans, physically and virtually, need a lot of attention.
An other factor is gossip, the people who gossip a lot often are not aware of the full story. Can make elders look quite foolish, can give you a number of examples if you are interested.
Not trying to say that all elders are dedicated and loving, only trying to make a point that it is extremely easy to criticise when you are not aware of the reasons for certain decision, and perhaps it is not such a bad idea to have full time ministers.