For the first time ever, I find myself disagreeing with noblegiraffe and Evil Twins.
Today is a sad sad day 
EvilTwins I am a Grammar School teacher (not a history teacher though!) and in both Grammars I have taught at, the castle making in history has been infamous-it is celebrated with a Show display and has always been thought of as a lovely thing to do.
It never occurred to me that some people would think that a homework other than writing something down on a piece of paper, would be pointless.
Just because some people are ‘not good at craft’ shouldn’t mean that automatically they should never do it. Surely the same as handwriting or writing essays or writing out maths equations? “Oh I’m not good still it so pointless for me!” A very convenient get-out clause...
If you want to know some of the reasons why those tasks are set from another teacher’s point of view:
Castle Making:
the research behind the different named components.
How they all fit together (such as a drawbridge) is basic engineering.
If a poster is created (they are not completely pointless) it can help label parts then be placed on the wall in the classroom to be seen daily.
Creating a PowerPoint:
If you knew the normally dire PowerPoints that are generated by students and some teachers alike (death by animation/copy and paste everything rather than bullet points/not embedding videos but using poor links etc.) then you would understand the need to practise this from a very early age.
Reading from a PowerPoint is a completely different skill than reading from a poem or story on a bit of paper. Sorry but it is. With a PowerPoint, you shouldn’t need to be holding paper and be reading from it or have your back to the classroom and just read out word for word what’s on the screen. I specifically teach students to be able to stand and face an audience and only briefly glance at the prompts in a PowerPoint to then speak out loud. Much much more different than just reading the exact words, in a line. This is easier to do when you have made the PowerPoint, rather than using someone else’s.
To dismiss a task as being pointless just because you don’t see a point in it, is extremely insulting to the teacher who has used their professional judgement to set a task.
My homework tasks, despite being a Computing teacher, are actually never using a computer (practical tasks are done in the lesson) but always handwritten as I need to be able to provide the practice for that as every test/public exam for the subject is on paper. However, I always get parents question why I never allow them to do a piece of homework on the computer to make it easier for them (far too easy to copy and paste!). You can’t win with everyone!