Companies subscribe to reports which provide "salary band" compensation data across the industry. When it's time to consider raises, management with access to those reports can then see if their pay is more-or-less in line with other similar companies.
This means titles like "Senior Engineer", "Staff Engineer" etc do actually have very meaningful purposes - they can be used to attempt to map together different levels at different companies in order to determine if you are being under- or over-paid for the role you are in.
If you've never held a management position that includes decisions around compensation increases you are likely unaware of quite how much thought and effort goes into this process.
Don't get me wrong: it sucks, and it's still mainly a bunch of tea-leaf reading (with serious real-world consequences for employees) - but it's important to understand this any time you're wondering why titles work the way they do.