Heyho!
Throughout the game, from farmers to investors, we're slowly progressing through the 19th century and ultimately entering the early 20th century, with certain innovations (e.g. machines, airships) and architectural achievements (e.g. skyscrapers) - we are not limiting us to e.g. everything up to 1870 or something. The small step into the early 19th century is intentional.
Additionally - and even more importantly: Anno games do take inspiration by real history, but are by no means aspiring to be historically accurate. The Anno world is its own thing, with its own characters, timelines and rules.
Of course it's fair to not like our approach, but comparisons with our real world history are only partially useful when Anno is set in its own world.