Confused why the Russians would use 3G/4G towers for their ERA secure communications

Confused why the Russians would use 3G/4G towers for their
ERA secure communications.

One FSB agent was apparently identified by his actual name, as a result
of a simple reverse-phone-lookup by Bellingcat of his cellphone number.

<https://latestpagenews.com/news/russians-wont-be-able-to-use-encrypted-phone-system-in-ukraine-after-destroying-pylons-expert-suggests/>=
  "The main explanation is that ERA required 3G or 4G to work 
   and the Russian Army destroyed those masts as they advanced"

Why would the Russians rely on the 3G/4G cell towers of another country for
_military_ secure communications inside that country during wartime C2?

It's baffling.
Maybe it's not true?

There are similar accounts on the net so if it's true that the ERA secure
communications use local 3G/4G cellular towers, my question is why would the
Russians design their secure communications to use local 3G/5G cell towers?

And even then, how did the typical SIM-carded cellphone work for that call?
-- 
REF
<https://securykid.com/russian-officer-complains-about-meltdown-of-communications-with-a-dead-general-on-an-intercepted-phone/>
<https://www.thedefensepost.com/2022/03/09/russian-phones-hacked/>
<https://www.datacenterdynamics.com/en/news/ukraine-russian-militarys-own-encrypted-phones-impacted-after-destroying-3g4g-towers-allowing-comms-to-be-intercepted/>
<https://inews.co.uk/news/world/russian-troops-era-phone-system-ukraine-destroyed-4g-masts-1504149>
<https://news.sky.com/story/russians-reportedly-take-out-own-secure-communications-system-during-kharkiv-assault-12560577>
<https://www.rawstory.com/russia-ukraine-war/>
<https://euroweeklynews.com/2022/03/08/russian-soldiers-called-idiots-for-destroying-3g-towers/amp/>
etc.