In Swift, why is "let _ = this" faster then "this != nil"?

So my question is why is let _ = this faster then this != nil?

Example:

This is:

let this : Bool? = true //

let start = DispatchTime.now()
for _ in 0...100000000  {
    guard this != nil else { continue }
}
let end = DispatchTime.now()

let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds
let timeInterval = Double(nanoTime)
print("Time \(timeInterval)") 

         // Time 5426559135.0
         // Time 5428084767.0
         // Time 5327325459.0

Slower than:

let this : Bool? = true //

let start = DispatchTime.now()
for _ in 0...100000000  {
    guard let _ = this else { continue }
}
let end = DispatchTime.now()

let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds
let timeInterval = Double(nanoTime)
print("Time \(timeInterval)")

          // Time 257045414.0
          // Time 261933863.0
          // Time 263465919.0