If a company came into being specifically to be Twitter's accountants or lawyers, it wouldn't be that big a deal. You might thinks it is risky or narrow, but you wouldn't be calling it a bubble.
If you really think these are just companies manufactured for sale to Twitter (not self evident, but granted for the sake of argument), you can think of it as just a variation of that.
If a company came into being specifically to be Twitter's accountants or lawyers, it wouldn't be that big a deal. You might thinks it is risky or narrow, but you wouldn't be calling it a bubble.
If you really think these are just companies manufactured for sale to Twitter (not self evident, but granted for the sake of argument), you can think of it as just a variation of that.