Liverpool completed the signing of the Portugal forward in a £41m deal, that could rise to £45m with add-ons, back in September.
The move represented a net outlay of about £30m for the Reds, with defender Ki-Jana Hoever moving the other way for £9m and a possible £4.5m in add-ons.
“It's not about business. For every season, even the head coach, we need to do some refreshment," Shi said, quoted by BirminghamLive, when explaining the decision.
"You always need some new blood. The Premier League is changing very fast and with the same squad you cannot handle everything. You can see the result, like Sheffield United.
“From a sporting and technical view we need to change every season. And sometimes a player needs to change having been in a city for four or five years.
“If Diogo stays here, I don't think he can perform at the same level that he is at Liverpool because it's a new environment with different teammates. That can spur him to do better.
“If it's to his own benefit, sometimes we have to change. Also if we can sell a player and get some profit in, then we can use the money to buy (players in) some other positions we need more.
“For the deal of Diogo Jota, I think it's the best deal of the five years because it's benefiting all three parties - the player, the buying club, the selling club."