haswell had more lanes (I believe 16) than that they were just tighter on what you could or couldnt disable that's generally built in like SATA ports, audio, LAN, etc
Skylake has 20 lanes when pretty much nothing from the chipset is enabled including SATA ports. The big change was DMI 2.0 to 3.0 which also got you PCI-E 3.0. If you remember 3 SATA III SSDs in RAID 0 was kind of the limit with DMI 2.0.
With the speed increase came more lanes basically enough for a M.2 without disturbing anything else. Just remember DMI 3.0 is still roughly PCI-E 3.0 x4 in total bandwidth.