Because PP is suitable for plastic injection parts as this style more, and most plastics are HDPE for blow job and production that does not have the flexibility and features of the PP is better than raekkrathaek.
The PP plastic suitable for injection rather than a piece of this style. And most of HDPE plastic is used for blowing the lid and produce no flexibility. And properties of PP to withstand shocks better than the first.
Because the plastic PP suitable for injection molding pieces to a style more like this and most of the plastic HDPE will go for a blow job and produce the lid without elasticity. And properties of PP to bear impact better than the first