It has to do with the tournament trying to keep competitive balanced opponents for as long as possible throughout the duration of the tournament. It's the same reason why the tournament distributes seeded players evenly into the draw to begin with so that they avoid high-profile matches until the later rounds of the tournament.
Related: See my answer about the makeup of tennis tournament draws here.
If Murray had not been seeded at all, then Lacko probably would have taken his place directly, instead of the shifting around of the draw that happened. But since Murray was seeded #2, it would throw off the distribution of competition in Murray's quarter of the draw to replace him with a lucky loser (LL). Now instead of playing Murray, his initial opponent (Sandgren) will play Cilic instead - which isn't much of a change in terms of the ranking and talent of the opponent.
The reason you might have seen the LL take the place of the player withdrawing in other tournaments is because the player withdrawing wasn't seeded. That's my guess, but if you can find a specific draw you're referring to maybe I can look at that case specifically.
You can read about the specific rules regarding the replacement of seeded players and lucky losers that starts at the bottom of page 24 of this document :
http://www.wimbledon.com/pdf/GS_Rulebook_2015.pdf
For tournaments sanctioned by the ATP (non-grand slam events) - see the ATP rulebook starting on page 106 for rules regarding the placement of seeds and vacancies: http://www.atpworldtour.com/-/media/files/rulebook/2017/2017-atp-rulebook_30dec16.pdf
