K Nutthapol,
I asked my guy why only EnTK and he said only this vendor wanted to perform this work for WD. He stressed this vendor delivered good quality and agreed this vendor perform better so far with the data provided.
Now, you ask me why others can't do.
I am happy that you get more vendors to do this work to compare to avoid single bid.
K Chatchai,
Mark down this concern and ask for all suppliers to bid from approved vendor list. If they do not want to submit quotation, ask purchasing's advice and documented the response.
Thanks,
Frankie