I think you misunderstand my point.
When a large company wants to raise cash for investment it has several options. It can borrow from a bank, and pay interest in return, or it can issue shares. Shareholders usually expect dividends.
In the case of BT, 65% of its outstanding shares are held by institutions like pension funds (figure from the London Stock Exchange), so anyone with a pension in such a fund benefits from BT dividends. That strikes me as much preferable to paying interest to bankers & their bonuses.
Without privatization any investment would have been financed by loans or by the taxpayer, and reluctance to do that was the cause of the chronic underinvestment. That's what Corbyn's dogma wants to take us back to.