1. I suppose some of these churches are just so used to it they don't think about it. Some of them probably hope "the next guy" will stick around longer. Some probably know it but don't say anything...a "don't ask don't tell" policy. May not be best for the churches, but it is unfortunately very common.
2. 10 years a reasonable tenure? I don't know if there's any set number...It would all depend on motivations and expectations.
In general, I think it could possibly not be all bad, if the churches saw that their church was playing a part in preparing a man for further ministry...whether there, or somewhere else.
Where it could be mostly bad is if said pastor planned to leave as soon as possible, and so as a result did not invest in the church, but rather did the minimum require to get by for a few years. I suppose it's the difference between seeing that church as a real place to minister and invest your life for a season of life, or rather as a stepping stone to be tossed aside at the earliest convenience.
