what do you think could be the technical factor to why Native SegWit address have lower tx fee than SegWit?
Just because P2SH pushes more data on-chain.
Native Segwit: bc1qspfmyevfh5apy66gqptg62h0c64pdyt8wdxx75
1. On-chain push in legacy output: 00149248e4c6f4ead8800bce8d27362d02d1b72be56d
2. On-chain push in legacy input: none needed, it is empty
3. On-chain push in witness space:
3.1. Signature: 304402201e50aca2e04654bdc7d66338de9ff3a1e675c1ccec4201166603eb2c8a3ff9700220415
d4adcea50222e804b9a32a25b38ef3aae1ea7631d32cb0a716e3caa07c2c001
3.2. Public key: 0291faef8450b7f98d5bf16a1296af64bfdb90bbba792ebb2f2b1e82c366e103bb
P2SH: 34XMxmELaDfXqevFWAM444WiCjrvA9sQXi
1. On-chain push in legacy output: a9141f14f1e0f2e741fed164960c8aaa673d24f87c0c87
2. On-chain push in legacy input: 16001442a62f734aa294c1aed7896d04d3bc979c77461c
3. On-chain push in witness space:
3.1. Signature: 30450221009498e0b0f30c2d9fded463eb81f9959d6de6dd9dbf3f623128f9ba13b9a5457602207
422b6b8f2416b41a5f5bcea13a87da38b4ecd15e52160015cf5cb2ba48240f001
3.2. Public key: 03ec6b23e5dce9b97bb35355d3376c5e89393f759c5db0eaf18b779ee3f3491d59
See? Native Segwit leaves no pushes in legacy input part (point 2), while P2SH always do so. And the consequence is simple: if you push more data, then you pay more fees.