In this simple example the Nose is in a G alignment on the Guard. If the slide is going to the defensive right the LT and LG are covered and therefore man scheme. The Center will start the slide. Good offensive linemen will help adjacent linemen when there is no threat to their gap. In this case the Center's A gap is directly threatened by the walked up LB. This threat prevents the Center from giving any initial help to the LG. The Nose now has a 1 on 1 inside rush lane from inside leverage vs. the LG.
In this example blitz both ILB's are walked up in their gaps. The slide is going to the defensive left. The RG is covered by the G front Nose therefore the RT and RG are man. The Center is starting the slide and is occupied thinking about the LILB who is in his A gap. The RB sees both the RILB and the SS walked up and is thinking he needs to get width to pick up whichever one of his dual read blitzes. The RB isn't focused on the Safety who is walking into the box presumable to play the 3RH drop in a fire zone coverage. Once the RB has gotten width and checked both his dual reads (ILB & SS) it will be difficult for him to redirect inside and block in the A gap. The Center has a chance to pick up the FS if he is athletic enough to redirect after sliding. If the Center or other offensive linemen start quickly let dropping LB's go to help elsewhere there is always a counter punch.
If OL are too aggressive to leave a dropping LB you can always fake that the LB is dropping and blitz him late. Here is video of a New York Giants blitz from their Superbowl victory over the Patriots. They ran these concepts consistently under defensive coordinator Steve Spagnuolo. This video is against Big on Big pass protection but is an excellent example of ways to create confusion for pass pro with LB's at or near the LOS.