Contamination can take place at the cleaning process as you mentioned. The tree bark harvested needs to be seasoned and if the cleaning is not done properly, TCA will lead to cork taint. But bottles if not sanitized properly before bottling can also lead to cork taint as research has shown. There are many different grades of corks, too. The more expensive one is likely to offer a guarantee to winery that there is no cork taint. For people who do not understand it, they might blame it on the winery. At a certain point, it is true that the winery is still responsible as better quality cork could have been chosen. That then leads to the pricing question.