Light rail is typically used in situations where it is fitting the trains into smaller spaces, often sharing space with other modes of transport. Building it to a heavier grade would cost more and offer no benefit. Even if you spend the money to build a light rail line to support a longer, heavier, faster train, you could not run that train anyway, because the spaces is shared, the turns may be too tight, the bridges may be too low, there may be no space for platforms. It is more cost and space effective to have separate lines.
Note, many light rail networks use standard gauges, so they can use standard maintenance equipment.
No, I believe it this way. It used to be one service that had access to everything it needs. Now it is microservices, so each microservice is caching a bunch of stuff, but of course all the wrong stuff, so every request requires at least one network call downstream. Thus more memory usage and slower.