These are the reasons I can think of why most especially large companies still won't accept bitcoin as a payment method:
1). Pseudonymous, It will be hard to trace the person behind a transaction .
2). Its past involvement with illegal activities (ex. Silk road )
3). Has a potential to be use and still being used for illegal activities .
4). Confirmation time getting slow and slow
5). No one controls it
I've been thinking about Pseudonymous, this is what really all about, unknown identity for every transaction and that is not good for the company. Sometimes I've been thinking too if pump and dump is also one of the disadvantages of bitcoin.
Because of this reason, the Bitcoin become more popular in online gambling. If we can track the transaction, then there is no difference b/w credit card and bitcoin transaction. our IT people can easily catch us because of online gambling activity. And I agree with one point the confirmation is getting slow day by day this is also one big disadvantage of Bitcoin.
That's true due to lot of transactions ,its confirmations becomes slower . Though still knowing that its transaction fees were not that high and sometimes free ,it is still worth it. Bitcoin still good in every services it offers.