Companies are made of people. There's no point of having loyalty to a company, because it's not the "company" that appreciates this loyalty (the company is just an inanimate thing), but your colleagues and managers who can appreciate. But most of these colleagues and managers don't share your loyalty. People jump ships at all levels, including sometimes at the CEO level.
So colleagues and managers don't appreciate loyalty per se. But they appreciate competence. And long tenure can increase someone competence in two ways: on one hand many companies sit on top of large and complex systems. With long tenure you not only get to be familiar with these systems, you start to know their history, you have your war stories, are familiar with past solutions to recurring problems, and not least, are able to teach new joiners. And on the other hand, you have an extensive network, which can increase your productivity tremendously, because in many cases the best solution to a problem is not to roll up your sleeves and work on it, but to ask a favor to a friend who can do it ten times faster than you.
Because of all these things, you'll see often people with 20 years or more of tenure being considered as pillars of their organization by their peers and managers.
Unfortunately, there are sometimes people with long tenure who are not that good, and don't have strong networks (because the strength of a network depends on how often you were able to help someone else). They are just "lifers". Competent enough that it's a headache for managers to replace them (and so they escape various rounds of layoffs), but not so competent to be appreciated and loved by their colleagues. Those people just attained "job security". Nobody appreciates their "loyalty", because it was not actually loyalty that made them stay in the same place.