No surprise as they both have a studious analytical approach to recruitment and both at present are punching above their weight and now contending a CL final at the same time.
I should also add Atletico who have the same approach and were unlucky to lose both finals against Real Madrid after conceding late equalisers in the dying minutes in both finals. Southampton are another club who also have the same analytical approach.
When you have such a recruitment based on analytics of signing players, net spends will be low as you sign players that go under the radar of big spending clubs.
Erikssen , Alli , Son, Mane, Salah, Robertson, Henderson, Coutinho, Firmino, Rose, Walker, Vertonghen ,all scream as analytically bought under valued players for a pressing style of play.
Both clubs got the right managers in perfect for that recruitment approach, signed the right players fit for their way of football, who's stats stuck out like sore thumbs for defensive metrics, running distance, pressing, sprints per game, and how good the players are in transition and both clubs are bearing fruit now.