either an organisation trains and equips their staff to work with company supplied equipment only, they accept the security risk inherent in demanding employees supply their own devices for corporate activities, or they ban all corporate activity outside the office (and all private devices from the office).
Each comes with a tradeoff, and the cost to the business of both the first and last option are far easier to calculate than the cost of the middle option, causing that one to be the one most often chosen.
It used to be the last one was the one most often chosen, but the cost of not allowing working on the move or from home has gone up so much, at the same time as the availability of relatively cheap laptops, notebooks, and smartphones that it's no longer a commercially viable option for most companies.
The best option for security would probably be option #1, have the company supply the equipment and train their staff in using it securely.
But even in companies that do supply equipment, the training is often forgotten or "postponed" (indefinitely) because of timing problems.
From personal experience I know that most people will not let their children use company owned equipment, and will be more careful with it than with privately owned equipment (even if it's identical equipment).
