CentOS 6.9 showed the following CPU flags in `/proc/cpuinfo`:

> fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat
> pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm
> constant_tsc up rep_good unfair_spinlock pni pclmulqdq ssse3 fma cx16
> pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave
> avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch arat xsaveopt
> fsgsbase bmi1 hle avx2 smep bmi2 erms invpcid rtm rdseed adx

I reinstalled CentOS 7.5 on the same machine, and got

> fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat
> pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm
> constant_tsc rep_good nopl eagerfpu pni pclmulqdq ssse3 fma cx16 pcid
> sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx
> f16c rdrand hypervisor lahf_lm abm 3dnowprefetch fsgsbase bmi1 hle
> avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap xsaveopt xsavec
> xgetbv1 arat

Why they are different?