(SPARQL) BIND fails with values from nested query - sparql

Question

I have been having problems with BIND IF in nested query (SPARQL). BIND fails and returns empty column (?koordColor) if I try to evaluate and bind value from inner query ?pop20 and ?pop14-?pop20 but is successful if I evaluate and bind ?pop14. Does anyone know how to fix this query so that I could evaluate and bind according to ?pop14-?pop20 value successfully?
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX qb: <http://purl.org/linked-data/cube#>
PREFIX lvcsb: <http://127.0.0.1:8080/LOD/>
PREFIX lvcsb-geo: <http://127.0.0.1:8080/LOD/territory/>
prefix opengis: <http://www.opengis.net/ont/geosparql#>
prefix lvl: <http://127.0.0.1:8080/LOD/statLevel/>
prefix xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?label ?koordColor ?koord ?pop20 ?pop14
WHERE {
?obs a qb:Observation.
?obs lvcsb:refPeriod 2014.
?obs lvcsb:refArea ?area.
?area lvcsb:version ?ver.
?ver rdfs:label ?label.
?ver opengis:Geometry ?geo.
?geo opengis:asWKT ?koord.
?obs lvcsb:population ?pop14.
BIND(IF(?pop14-?pop20 > 1000, "green", "blue") AS ?koordColor)
{SELECT ?label ?pop20 WHERE {
?obs a qb:Observation.
?obs lvcsb:refPeriod 2020.
?obs lvcsb:refArea ?area.
?area lvcsb:version ?ver.
?ver rdfs:label ?label.
?obs lvcsb:population ?pop20.
{SELECT distinct ?label where{
?obs a qb:Observation.
?obs lvcsb:refArea ?area.
?area lvcsb:version ?ver.
?ver rdfs:label ?label .
?ver lvcsb:statLevel ?level .
filter(?level = lvl:4 )
filter(lang(?label)='lv')}
}}
}}