There can be many reasons why a cabinet cannot simply be placed next an existing cabinet.
1) Other utility services; gas, electric, water, telecoms etc. can be found all over the place be it beneath the highway (carriageway, footway or verge) and on private property adjacent to the highway. It's often far simpler, quicker and cheaper for Openreach to locate a cabinet elsewhere than to get another utility to move existing services. - For this location:
https://www.google.co.uk/maps/@53.6404128,-1.336225,3a,49y,92.33h,82.29t/data=!3m6!1e1!3m4!1swPYF6PPy4tSkmoAGx_ErwQ!2e0!7i13312!8i6656 to the left of the existing cabinet you've got the telegraph pole (and any ducting that might link back to the PCP), further left you an electrical shed/substation so potential low/high voltage cables.
In the case of the current Virgin Media rollout in Thanet, the contractors also have guidelines on how far/close they can place cabinets to existing apparatus.
2) Highway Authority issues; although for the most part, telecom utilities are operating under the Electronic Communications Code (
https://www.ofcom.org.uk/phones-telecoms-and-internet/information-for-industry/policy/electronic-comm-code) when it comes to installing apparatus in the public highway, they can be advised or even instructed to re-locate or move apparatus if they pose issues with sight lines at junctions for example.
This is an example of a poorly sited cabinet located at the junction of two roads, on a slopped footway (taking up a good size of the width of the footway) and directly outside of a retirement home. This cabinet was moved by Openreach after Kent County Council Highways instructed them to do so. -
https://www.google.co.uk/maps/@51.3843871,1.4007249,3a,74.2y,92.45h,70.85t/data=!3m6!1e1!3m4!1st9_mnDwivhrfsIKEF3axfg!2e0!7i13312!8i6656From what I can recall, the proposed location of the cabinet wasn't for it to be located on the junction where it ended up being installed. The PCP for the cabinet was only just up the road near the end of the bus clearway
https://www.google.co.uk/maps/@51.3842659,1.4012713,3a,75y,324.82h,73.61t/data=!3m6!1e1!3m4!1s5S6lJlr_wx0Qf_eWJ8WeTQ!2e0!7i13312!8i66563) Resident objections, issues etc.; On occasions there may be valid reasons for a resident/home owner to complain about the location of a cabinet though, with the majority of cabinets not requiring planning permission, the normal process of objecting at the planning stage won't apply.
In this location:
https://www.google.co.uk/maps/@53.6404128,-1.336225,3a,49y,92.33h,82.29t/data=!3m6!1e1!3m4!1swPYF6PPy4tSkmoAGx_ErwQ!2e0!7i13312!8i6656 placing a cabinet against the wall to the right of the PCP may draw arguments from the home owner that it could increase the risk of people breaking into the property by getting easier access over the wall.