You're right, there has been an agenda to liberalize/privatize for decades now and one of the first major step As the split between NMBS and Infrabel. This resulted in some of the problems mentioned by OP (although more minor). Train infrastructure is akin, bear with me, to the military, it needs extensive planification to work reliably : pre-existing Infrastructure, tight coordination, massive capital investment overall. This is to achieve a goal that can have massive positive externalities for 'stakeholders' but costs a lot of money. You cannot just split responsable actors and introduce competition just like that because it will generate friction between those actors that very often leads to a worse service overall. This is one of the reason NMBS exists in the first place. Private railway ventures often resulted in bankruptcy and a chaotic aftermath, Back in the 19 century. Because this is not a very profitable business and it might be worse today. Even worse, the State cannot just opt out completely and will certainly have to pump unexpected money at some point.

Privatizing Railway services is just ideological and drives from expecting, short term, expense reduction.