I think it's because it's not the same "some". When "some" means an indefinite quantity, "some milk", it has no translation in Indonesian. I have drunk some milk, is the same than I have drunk milk.
When you have some meaning that you have several objects, in few quantities, it's translated with "beberapa".
Beberapa orang, beberapa tomat, etc...
Karena, Drank di gunakan apabila kejadian itu berulang atau kebiasaan "I drank a glass of water every day (Saya minum segelas ait setiap hari) Sedangkan, Drink di gunakan apabila kejadian itu telah berlalu (tenses perfect) " i have drunk some milk (Saya telah meminum susu)
Lebih jelas nya Anda bisa membacany di sini https://www.ilmubahasainggris.com/perbedaan-drink-drank-drunk-drinking-beserta-contoh-kalimat-dalam-bahasa-inggris/