These things are true for any infection – my wife recently had a non-covid cold and despite several nights snuffling next to me, nothing. It's common. Some people simply don't get infected, viruses have to get to their favourite cell, and get inside, which is a complex series of events, and there's genetic variability in receptors etc. Even if a virus finds its way into the cell, it then has to replicate at high levels, which means it needs to hijack the cell. Cells don't just hand over their keys willingly. And then finally, the results might simply be asymptomatic (much of the symptomatology of any viral infection is your immune system) a virus may simply do its thing without you noticing (the vast majority of viruses do just this, you don't know you have them).