Simple. Because it got slower over time.

All these threads about software being worse and "perceptually slower" than it used to are about regressions. Google Maps and other mentioned tools aren't pushing the envelope. They aren't bleeding edge. They were science fiction made manifest 10-15 years ago, and since then actually decayed in utility, ergonomics and performance. Meanwhile, all the money invested in all the software and hardware should have given us the opposite outcome.

While utility and ergonomics can be debated, I'd be surprised if performance of Google Maps in particular has regressed. Google keeps track of latency metrics for every one of its thousands (millions?) of services. If the services involved in Google Maps began to regress in latency, it would have been noticed and addressed. You can be sure that many performance improvements have been implemented, and if you had access to the 2005 and 2019 versions, you would be amazed at how capable and fast today's is compared to then.

I don't have access to 2005 vs. 2019 versions to Google Maps to compare, but I really don't care about latency as much as I care about local performance. Google Maps is getting noticeably heavy over time.

What I have good memory about though is GMail. I've been using it for 10+ years now and that really keeps getting slower and heavier over time, while offering no extra functionality to compensate.

Google may track latency metrics for all their services, yet somehow, the stuff they do is one of the most bloated stuff out there. I guess they don't look at, or care, about those metrics.

I get your point, and it has its merit, but at some point you'd expect things to slow down, right?

My experience makes me expect it, on the theory that popular software sucks and companies building it tend to have broken incentive structures.

It shouldn't be like this in theory. Computers only ever get faster (occasional fixes for CPU bugs notwithstanding). So making software slow down requires active work. So does removing or breaking useful features.