A lot of materials aren't what they used to be, Brian.
At one of the wildlife reserves where I regularly record we made some bird boxes from supposed marine grade plywood. At the time, I questioned its quality and said they should have purchased the material from a boatbuilder not a general builders merchant. After 2 years the plywood has started to delaminate.
I have been experimenting with making some replacement bird boxes for that area because the current wooden ones will need replacing soon. I am working with a mixture of plastic soil drainage pipes and HDPE sheet plastic. The first ones are due to be erected over the next few days. The first prototype used an old plastic kitchen chopping board instead of new HDPE.
Several years ago they acquired some boxes constructed from a mix of concrete and sawdust which have proved to be excellent but at a cost of around £25 each they are unaffordable for a nature trust with 40 boxes on just that site.
Last year, as an experiment, I tried a couple of those very cheap small boxes which are available from garden centres and from various internet sites. Neither was used last year and I doubt there will be any interest this year. But you have to test these things just in case they might work.