AIs will be strong / have sentience because the easiest path to creating AIs that are that capable is to throw lots of computing power at the problem: simulate and then emulate specific human brains and use those resulting in silico entities as a starting point for further alterations and enhancements towards specific end goals.

That level of computing power will be available long before the nature of sentience is understood, probably within the next 15 years, and there are already heavily funded scientific projects that are starting down that road.

That doing it this way is enormously unethical isn't going to stop people from going down this road: the potential economic gains of creating knowledge workers to order are vast, and there are already philosophies (e.g. identity as pattern) that can be adapted to suggest that instantiating and destroying - or even just running - large numbers of in silico sentiences doesn't amount to mass murder. Therefore some groups will adopt those philosophies and prosper from the gains.