Two remarks:
Firstly: The coins you list as "Occupied Germany (5 pfenning, 1949; 50 pfenning, 1949)" are not correctly distinguished from the West-Germany ones, as despite the 1949 date and "Bank Deutscher Länder" Inscription, these coins were issued into circulation not before January 1950, well after West-Germany was founded (and continued to be occupied afterwards). (5 Pfenning was put into circulation 2nd January 1950, while 50 Pfenning was put into circulation on 14th February 1950).
Only the 1 Pfennig (24th January 1949) and the 10 Pfennig coins (21st May 1949) of that series were issued in 1949 before the founding of West-Germany (23rd May 1949) and thus circulated in the three western occupation zones (even if only for less than 48 hours in case of the 10 Pfennig, considering that the issue date was a Saturday and people were likely not lining up at midnight to get them new coins).
All “Bank Deutscher Länder” Coins were frequently found in circulation until the switch to the Euro in 2002. They were quite easy to spot, due to usually showing higher wear than the ones issued later. Only had to be sorted from the 1950 Pfennig coins that showed similar wear.
Secondly: Shortly before reunification, the West-German coins already in circulation (including the remaining Bank Deutscher Länder coins) simply became legal tender in the GDR; and after reunification, Berlin was added as additional mint for new coins (mintmark A).
The types you show for “Reunified Germany (5 pfenning, 1995; 2 Deutsche mark, 1990)” are types that were first minted in 1967/8 and 1988, respectively. There are no circulation coins that were issued exclusively for reunified Germany, unless you count 2 DM Willy Brandt, which was first issued in 1994 by all five mints, itself being the final issue of the famous politicians series, replacing the “Kurt Schumacher” Design used since 1979 to limit the parallel issues to three types.
If you are interested in this topic and want a complete historic set, you should also look for a real Allied occupation coin issued between 1945 and 1948 (KM#A103, A104, A105), which are similar to the 1, 5 and 10 Reichspfenning in design and material (zinc), but quite obviously without the swastika below the eagle. They are usually the hardest types to find due to low mintage compared to other types. They have strange numbers with an “A” prefix because even the publishers overlooked them at first when assigning the numbers for the KM catalogue.
N#15267
Regarding the question why West-Germany had the same metals as before, while East Germany got cheap aluminum scraps for coins: Easy. Everything remotely valuable, be it raw materials or valuables (even infrastructure like railway lines deemed unnecessary by the occupiers), was taken or prioritized for the soviet union. The soviet vassal states (Eastern Europe) were litearally plundered and drained of ressources for decades during the occupation, while western Europe recovered due to the Marshall-plan. It was common in GDR to have electric wiring in the house made of aluminum instead of copper for the same reason (and of course almost no landline phones in the private houses, as those also required copper wiring at the time).