This is clock work, every election period they shutdown social media & electronic payments. It happened in 2016[0]
But when an "OTT" tax was imposed on social networks (Whatsapp, Twitter, Facebook, Snapchat, Linkdin) in 2018[1].
Majority didn't want to pay an extra tax(required to use social media) on top of paying for internet. So majority learnt how to use vpns.
As a result, the OTT tax was a complete failure [2] and now the Uganda Revenue service is planning on bundling it with internet data costs.
Since people now know how to use vpns, social media cant be blocked.
So the reason for blocking smartphone app stores is to essentially, STEP 1 i.e Stop people from installing VPNs.
STEP 2 will probably be the total blocking of all social media.
[0]:https://theatlantic.com/amp/article/463407/
[1]:https://dw.com/en/uganda-one-year-of-social-media-tax/a-4967...
[2]:https://techjaja.com/ott-tax-fails-as-ura-proposes-tax-on-in...