Wikidata COUNT(*) query times out

Question

I have a straightforward query that counts how many humans have an English Wikipedia page.

prefix schema: <http://schema.org/>
PREFIX wikibase: <http://wikiba.se/ontology#>
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?item ?article
WHERE 
{
  ?item wdt:P31 wd:Q5 . # Must be of a human
  ?article schema:about ?item ; # Must have a Wikipedia article
           schema:inLanguage "en" ; # Article must be in English
           schema:isPartOf <https://en.wikipedia.org/> . # Wikipedia article must be regular article
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". } # Helps get the label in your language, if not, then en language
}

I get expected output as follows:

 wd:Q11124  <https://en.wikipedia.org/wiki/Stephen_Breyer>
 wd:Q10727  <https://en.wikipedia.org/wiki/Steve_Leo_Beleck>
 wd:Q10065  <https://en.wikipedia.org/wiki/Taichang_Emperor>
 wd:Q9605   <https://en.wikipedia.org/wiki/Sarah_Allen_(software_developer)>

However, if I change the SELECT statement from

SELECT ?item ?article

to

SELECT (count(?item) as ?count)

I get timeout error. Please note that the count statement works if I only specify "human" condition and exclude English Wiki article condition. So, clearly, some kind of background join is causing the query to timeout.

However, this is a fairly trivial join, so the query timeout is surprising.

Please let me know what may I be missing here.

Thanks!