It makes no sense at all that the US Capitol doesn't have stronger barriers between the public areas and the private offices. Every bank or other large company has such a setup for information security reasons.
Dutch representatives are accessible by the people. They have a walk-in hour, you can call them, email them, write them, you can join hearings and meetings where they're present, they go out into the country to talk to citizens. But what you can't do is waltz into their office. This has obvious reasons in a post 9/11 world, and it has nothing to do with the fact the Netherlands has a king who has a purely symbolic function and does not participate in politics, no different from say France which is a republic, or Germany which saw a mob storm the Reichstag a few months ago and was easily held off by the police, which is also a republic.
https://www.dormakaba.com/resource/blob/128222/7d74af646dce4...
They're configured one-way only, can be fully opened for high through-put or emergencies, but are otherwise single-person only. They can detect multiple people in various ways. The default for sensitive areas would be biometric (e.g. weight, some parlement members coming back from vacation a little overweight have had to get a manual override in the past). Of course bulletproof, and can be controlled at a distance by an operator.
It makes sense that not everything requires something like this, but the office of the speaker of the house of course should be in any situation. If she wishes to meet people in less-secure rooms it's entirely possible to create meeting rooms with fewer or even no significant entry or security controls if you wish, but your personal office, places where you store sensitive data etc... can't just have em behind a few wooden doors.
Of course some countries opted for the benefit of a modern building. The capitol is more than two centuries old, you can only retrofit it so much.