I think the recruiters are covering themselves with the employers who are their clients - they're afraid that they could be blamed if you took a permanent position then DIDN'T get a further visa, so leaving the employer in the lurch.
The fact remains that there are hundreds of people in the same circumstances as you who HAVE been put forward for permanent positions. And people who hold a work visa in their own right have to renew their visas periodically - they have their job offer in the first place despite the fact that the work visa will run out.
The answer to this probably comes down to talking hard till you convince somebody, and/but you won't convince everybody.
All the best.