Why is it that so many products, in particular electronic or tech products (international brands) don't have manufacturers warranty for the standard 1 year when bought in Thailand. I have seen items that specify only a ' local warranty ". And guess that means it is in the country only. Do manufacturers not issue a standard warranty when they sell in Thailand for some reason ?

Lucky to get it at all in many cases, and then it's only 7 days return ! for many items/retailers.

 

I suspect that some items are rejects, grade b,c etc that don't pass for the west and are sold off in the east.

Different products are produced at different standards, specifications and price-point for different markets. 
 

The price of the product includes the cost of the warranty, so it makes little sense to provide a high cost warranty for a product that sold at a price that did not include it. 
 

Also, they may not have the parts to support it outside the area, and while the items may look identical, they could be very different internally. 
 

All that said, I’ve generally had good warranty service in Thailand.