Why are African governments blocking phone lines of citizens?

Al Jazeera :
This Monday, millions of Nigerians woke up to find that they had been barred from making phone calls. The number of disconnected lines is reported to be as many as 75 million, more than a third of the total 198 million lines nationwide.
In December 2020, Abuja issued a directive for all SIM card carriers to link their lines to a unique National Identity Number, citing a need to tackle the plaguing insecurity in the country.
That deadline was postponed numerous times but last week’s attack on a train by armed groups was a wake-up call. When reports started surfacing online that the attackers had started calling families of abducted passengers for ransom, the government swung into action, fulfilling its almost two-year-old promise to cut off non-compliant citizens.
On social networks, many – especially southerners – are debating the connection between SIM card linkage with the national identity number and the actions of these groups, known locally as bandits, whose axes of focus are swaths of the northwest and central Nigeria.
In 2015, the Nigerian government fined MTN, one of the continent’s biggest telecom players, $5.2bn for defaulting in cutting off unverified customers. The National Communications Commission (NCC) had previously instructed the telecom giant to deactivate between 10 and 18.6 million lines. But government swung into action after the high-profile kidnap of a former Nigerian finance minister; police say the kidnappers used MTN lines to contact his family members.
Across the continent, there is a lengthening line of governments embarking on a mass disconnection drive citing, among other things, domestic security. In March, Zambia announced it had deactivated two million SIMs cards to stem the volume of fraud carried out using mobile lines.
Kenyan media have also reported an April 15 deadline by authorities in the East African country for the deactivation of unregistered SIM cards – the third such deadline in the past 10 years. In 2013, it switched off more than two million SIM cards after an attack by the armed group al-Shabab.
Last year, Tanzania said it had blocked 18,000 SIM cards involved in criminal activities. In a bid to also curtail mobile scams, Ghana issued a directive for every SIM card carrier to re-register their SIMs with the Ghana Card, the national residency card, or lose them.