still most of companies dont go with open source for comercial production.
Actually, quite a few companies do rely on open source for commercial products. Rarely will it be advertised on the box, because most (e.g. 99% who are not engineers) consumers do not care.
they start writting code from basic or BUY costaly library or adk.
Sometimes it is because the company, or the engineering team at that company, wants/needs support. Commercial support comes with financial commitments, open source support does not.
Sometimes it is because open source libraries are not complete.
Sometimes it is because open source licenses means revealing work the engineering team has done, and the company does not wish that to happen.
Sometimes engineers simply don't know about an open-source option.
why is there any disadvantage of arduino. is arduino usrd for comercial perpose in your country.
There are always trade-offs. The "disadvantages" depends on your situation.
This, like all engineering puzzles, isn't a "black and white" or "yes/no" kind of thing. You must look at multiple elements and determine the best solution. The idea "BECAUSE ITS OPEN SOURCE!!!!" is not always the best solution for a given problem.