Postgres not using index in simple query - postgresql

Question

I have a simple table storing a few values.
create table customer_usage
(
id bigserial not null
constraint customer_usage_pk
primary key,
customer_id bigint not null
constraint customer_usage_customer_id_fk
references crm.customer,
profile_id bigint not null,
supplier_id bigint not null,
direction smallint not null,
pod varchar not null,
trunced_date date not null,
period_end timestamp with time zone not null,
usage_wh real not null,
created_at timestamp with time zone default now() not null
);
create unique index customer_usage_id_uindex
on customer_usage (id);
create index customer_usage_profile_id_index
on customer_usage (profile_id);
create index customer_usage_supplier_id_index
on customer_usage (supplier_id);
create index customer_usage_trunced_date_index
on customer_usage (trunced_date);
alter table edm.customer_usage cluster on "customer_usage_trunced_date_index";
When I try to query data for for a specific "trunced_date" the explain plan shows, that it is NOT using the clustered index for this very column.
explain analyze select * from edm.customer_usage where trunced_date = '2021-05-26';
Explain plan:
QUERY PLAN
Seq Scan on customer_usage (cost=0.00..48792.40 rows=1495664 width=92) (actual time=0.053..20115.107 rows=1494912 loops=1)
Filter: (trunced_date = '2021-05-26'::date)
Rows Removed by Filter: 254880
Planning Time: 0.370 ms
Execution Time: 37914.739 ms
I don't understand, why -- in the simplest query asking specifically for one column that has a clustered index -- this index is not used.
Thank you very much for your help.
Fritz