Why is a straight-in approach not allowed to RWY 07 at Cluj (LRCL)?
It is allowed.
Runway 07 has a published GNSS straight-in instrument approach as of 10 Nov 2016.

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For non-GNSS equipped planes, there are no published straight-in instrument approaches for runway 07. Only the circling VOR 07.
However, in VMC the crew may request or likely be given a visual straight-in approach to 07.
As to why there aren't published minima for a straight-in VOR approach to runway 07, I can think of two plausible reasons:

VOR accuracy being not good in that quadrant, maybe due to terrain interference, or interference from the tall church on short final.
Winds almost always favor 25, so no effort was made to certify a straight-in approach using VOR for 07.


When an aircraft intends to land on a runway for which no instrument approach procedure exists, it may descend on the instrument approach to another runway and, provided the required visual references are established at the circling MDA/H, maneuver visually for landing on the desired runway. This procedure is used when landing on the instrument runway is undesirable, due for example to wind conditions or work in progress.
[...]
A circling approach is the visual phase of an instrument approach to bring an aircraft into position for landing on a runway which is not suitably located for a straight-in approach.
— skybrary.aero